Allow importing of r/github_repository_autolink_reference by key prefix

[marc-sensenich]

Allow importing of r/github_repository_autolink_reference by key prefix to allow for simpler import operations for GitHub admins as they'll be able to import based on something they know, the key prefix, instead of something they may need to look up, the autolink ID

Local acceptance test status

TF_ACC=1 go test -v ./... -run TestAccGithubRepositoryAutolinkReference      
?       github.com/integrations/terraform-provider-github/v4    [no test files]
=== RUN   TestAccGithubRepositoryAutolinkReference
=== RUN   TestAccGithubRepositoryAutolinkReference/creates_repository_autolink_reference_without_error
=== RUN   TestAccGithubRepositoryAutolinkReference/creates_repository_autolink_reference_without_error/with_an_anonymous_account
    resource_github_repository_autolink_reference_test.go:54: anonymous account not supported for this operation
=== RUN   TestAccGithubRepositoryAutolinkReference/creates_repository_autolink_reference_without_error/with_an_individual_account
=== RUN   TestAccGithubRepositoryAutolinkReference/creates_repository_autolink_reference_without_error/with_an_organization_account
=== RUN   TestAccGithubRepositoryAutolinkReference/imports_repository_autolink_reference_without_error
=== RUN   TestAccGithubRepositoryAutolinkReference/imports_repository_autolink_reference_without_error/with_an_anonymous_account
    resource_github_repository_autolink_reference_test.go:102: anonymous account not supported for this operation
=== RUN   TestAccGithubRepositoryAutolinkReference/imports_repository_autolink_reference_without_error/with_an_individual_account
=== RUN   TestAccGithubRepositoryAutolinkReference/imports_repository_autolink_reference_without_error/with_an_organization_account
=== RUN   TestAccGithubRepositoryAutolinkReference/imports_repository_autolink_reference_by_key_prefix_without_error
=== RUN   TestAccGithubRepositoryAutolinkReference/imports_repository_autolink_reference_by_key_prefix_without_error/with_an_anonymous_account
    resource_github_repository_autolink_reference_test.go:150: anonymous account not supported for this operation
=== RUN   TestAccGithubRepositoryAutolinkReference/imports_repository_autolink_reference_by_key_prefix_without_error/with_an_individual_account
=== RUN   TestAccGithubRepositoryAutolinkReference/imports_repository_autolink_reference_by_key_prefix_without_error/with_an_organization_account
=== RUN   TestAccGithubRepositoryAutolinkReference/deletes_repository_autolink_reference_without_error
=== RUN   TestAccGithubRepositoryAutolinkReference/deletes_repository_autolink_reference_without_error/with_an_anonymous_account
    resource_github_repository_autolink_reference_test.go:193: anonymous account not supported for this operation
=== RUN   TestAccGithubRepositoryAutolinkReference/deletes_repository_autolink_reference_without_error/with_an_individual_account
=== RUN   TestAccGithubRepositoryAutolinkReference/deletes_repository_autolink_reference_without_error/with_an_organization_account
--- PASS: TestAccGithubRepositoryAutolinkReference (54.28s)
    --- PASS: TestAccGithubRepositoryAutolinkReference/creates_repository_autolink_reference_without_error (17.37s)
        --- SKIP: TestAccGithubRepositoryAutolinkReference/creates_repository_autolink_reference_without_error/with_an_anonymous_account (0.00s)
        --- PASS: TestAccGithubRepositoryAutolinkReference/creates_repository_autolink_reference_without_error/with_an_individual_account (9.02s)
        --- PASS: TestAccGithubRepositoryAutolinkReference/creates_repository_autolink_reference_without_error/with_an_organization_account (8.35s)
    --- PASS: TestAccGithubRepositoryAutolinkReference/imports_repository_autolink_reference_without_error (18.34s)
        --- SKIP: TestAccGithubRepositoryAutolinkReference/imports_repository_autolink_reference_without_error/with_an_anonymous_account (0.00s)
        --- PASS: TestAccGithubRepositoryAutolinkReference/imports_repository_autolink_reference_without_error/with_an_individual_account (9.42s)
        --- PASS: TestAccGithubRepositoryAutolinkReference/imports_repository_autolink_reference_without_error/with_an_organization_account (8.92s)
    --- PASS: TestAccGithubRepositoryAutolinkReference/imports_repository_autolink_reference_by_key_prefix_without_error (18.01s)
        --- SKIP: TestAccGithubRepositoryAutolinkReference/imports_repository_autolink_reference_by_key_prefix_without_error/with_an_anonymous_account (0.00s)
        --- PASS: TestAccGithubRepositoryAutolinkReference/imports_repository_autolink_reference_by_key_prefix_without_error/with_an_individual_account (8.91s)
        --- PASS: TestAccGithubRepositoryAutolinkReference/imports_repository_autolink_reference_by_key_prefix_without_error/with_an_organization_account (9.11s)
    --- PASS: TestAccGithubRepositoryAutolinkReference/deletes_repository_autolink_reference_without_error (0.56s)
        --- SKIP: TestAccGithubRepositoryAutolinkReference/deletes_repository_autolink_reference_without_error/with_an_anonymous_account (0.00s)
        --- PASS: TestAccGithubRepositoryAutolinkReference/deletes_repository_autolink_reference_without_error/with_an_individual_account (0.28s)
        --- PASS: TestAccGithubRepositoryAutolinkReference/deletes_repository_autolink_reference_without_error/with_an_organization_account (0.27s)
PASS
ok      github.com/integrations/terraform-provider-github/v4/github     54.653s
                                                     

Closes #947