Adds autocomplete flag options to plan and apply

[absolutelightning]

Fixes - https://github.com/hashicorp/terraform/issues/34396

Terraform plan and apply is possibly the most popular commands. This PR adds auto-complete for flag options. When user types terraform apply / terraform plan followed by - the auto-complete flag options are visible to him.

Auto complete flag options created in this PR is from help section of the command.

Target Release

1.6.x

Draft CHANGELOG entry

ENHANCEMENTS

asheshvidyut@asheshvidyut-H2GX766V9T ~/terraform (gh-issue-34396) » ./bin/terraform apply -                                                     130 ↵
-auto-approve      -compact-warnings  -input             -lock-timeout      -parallelism       -state-out
-backup            -destroy           -lock              -no-color          -state

asheshvidyut@asheshvidyut-H2GX766V9T ~/terraform (gh-issue-34396) » ./bin/terraform plan -                                                      130 ↵
-compact-warnings     -generate-config-out  -lock-timeout         -parallelism          -replace              -var
-destroy              -input                -no-color             -refresh              -state                -var-file
-detailed-exitcode    -lock                 -out                  -refresh-only         -target