Add terraform validator

[manitgupta]

• Adds a Terraform Validator for Terraform samples being added to the repo. It verifies the sample structure and the plan generated for it via terraform validate.
• Formats the existing bulk migration example to comply with Terraform validator using terraform fmt.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 45.51%. Comparing base (e678faf) to head (fc895d6). Report is 10 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1663 +/- ## ============================================ + Coverage 41.25% 45.51% +4.26% + Complexity 2928 717 -2211 ============================================ Files 763 301 -462 Lines 44372 16176 -28196 Branches 4752 1609 -3143 ============================================ - Hits 18307 7363 -10944 + Misses 24521 8271 -16250 + Partials 1544 542 -1002 ``` | [Components](https://app.codecov.io/gh/GoogleCloudPlatform/DataflowTemplates/pull/1663/components?src=pr&el=components&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GoogleCloudPlatform) | Coverage Δ | | |---|---|---| | [spanner-templates](https://app.codecov.io/gh/GoogleCloudPlatform/DataflowTemplates/pull/1663/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GoogleCloudPlatform) | `59.05% <ø> (-2.32%)` | :arrow_down: | | [spanner-import-export](https://app.codecov.io/gh/GoogleCloudPlatform/DataflowTemplates/pull/1663/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GoogleCloudPlatform) | `∅ <ø> (∅)` | | | [spanner-live-forward-migration](https://app.codecov.io/gh/GoogleCloudPlatform/DataflowTemplates/pull/1663/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GoogleCloudPlatform) | `73.88% <ø> (ø)` | | | [spanner-live-reverse-replication](https://app.codecov.io/gh/GoogleCloudPlatform/DataflowTemplates/pull/1663/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GoogleCloudPlatform) | `49.66% <ø> (ø)` | | | [spanner-bulk-migration](https://app.codecov.io/gh/GoogleCloudPlatform/DataflowTemplates/pull/1663/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GoogleCloudPlatform) | `82.07% <ø> (ø)` | | [see 479 files with indirect coverage changes](https://app.codecov.io/gh/GoogleCloudPlatform/DataflowTemplates/pull/1663/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GoogleCloudPlatform)

[bharadwaj-aditya]

Can you add some comments/ docs with use cases on the create sample TF scipt?

[manitgupta]

Can you add some comments/ docs with use cases on the create sample TF scipt?

As in comments/docs on the samples that will follow?

[manitgupta]

This is independent of that and is only localised to Spanner specific templates.

The existing auto-generated template only focuses on Dataflow while the samples we will add will focus on other resources relevant to an IaaC configuration with respect to the Spanner templates.