Serialize data_json as well as data on read of kvv1

[joey-squid]

Description

When reading a kvv1 secret, this PR updates both data_json and data (previously this was just data). This catches any discrepancies and drifts.

Note that this may cause diffs to appear where they didn't before. This is because the diffs were always there but ignored by default.

Closes #2143

Checklist

• [x] Added CHANGELOG entry (only for user-facing changes)
• [ ] Acceptance tests where run against all supported Vault Versions

Output from acceptance testing:

$ make testacc TESTARGS='-run=TestAccKVSecret'
Test and changelog
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test -run=TestAccKVSecret -timeout 30m ./...
?   	github.com/hashicorp/terraform-provider-vault	[no test files]
?   	github.com/hashicorp/terraform-provider-vault/cmd/coverage	[no test files]
?   	github.com/hashicorp/terraform-provider-vault/cmd/generate	[no test files]
?   	github.com/hashicorp/terraform-provider-vault/helper	[no test files]
?   	github.com/hashicorp/terraform-provider-vault/internal/consts	[no test files]
?   	github.com/hashicorp/terraform-provider-vault/internal/identity/group	[no test files]
?   	github.com/hashicorp/terraform-provider-vault/internal/identity/mfa	[no test files]
?   	github.com/hashicorp/terraform-provider-vault/internal/pki	[no test files]
ok  	github.com/hashicorp/terraform-provider-vault/codegen	(cached) [no tests to run]
ok  	github.com/hashicorp/terraform-provider-vault/internal/identity/entity	(cached) [no tests to run]
?   	github.com/hashicorp/terraform-provider-vault/internal/sync	[no test files]
?   	github.com/hashicorp/terraform-provider-vault/schema	[no test files]
ok  	github.com/hashicorp/terraform-provider-vault/internal/provider	(cached) [no tests to run]
ok  	github.com/hashicorp/terraform-provider-vault/testutil	(cached) [no tests to run]
ok  	github.com/hashicorp/terraform-provider-vault/util	(cached) [no tests to run]
ok  	github.com/hashicorp/terraform-provider-vault/vault	4.236s

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[hashicorp-cla]

All committers have signed the CLA.

[joey-squid]

Not sure how to run tests against other versions of Vault. (I'm also not sure my change is even correct, but that's a different story :) )

[fairclothjm]

Superseded by https://github.com/hashicorp/terraform-provider-vault/pull/2207