feat: Convert multi replication specs multi regions advanced clusters

[lantoli]

Description

Convert multi replication specs multi regions advanced clusters

• Other conversions such as with dynamic blocks will be done in follow-up PRs
• Documentation will be updated in follow-up PRs

Link to any related issue(s): CLOUDP-339184

Type of change:

• Bug fix (non-breaking change which fixes an issue). Please, add the "bug" label to the PR.
• New feature (non-breaking change which adds functionality). Please, add the "enhancement" label to the PR. A migration guide must be created or updated if the new feature will go in a major version.
• Breaking change (fix or feature that would cause existing functionality to not work as expected). Please, add the "breaking change" label to the PR. A migration guide must be created or updated.
• This change requires a documentation update
• Documentation fix/enhancement

Required Checklist:

• I have signed the MongoDB CLA
• I have read the contributing guides
• I have checked that this change does not generate any credentials and that they are NOT accidentally logged anywhere.
• I have added tests that prove my fix is effective or that my feature works per HashiCorp requirements
• I have added any necessary documentation (if appropriate)
• I have run make fmt and formatted my code
• If changes include deprecations or removals I have added appropriate changelog entries.
• If changes include removal or addition of 3rd party GitHub actions, I updated our internal document. Reach out to the APIx Integration slack channel to get access to the internal document.

Further comments

[Copilot]

Pull Request Overview

This PR converts Terraform configuration blocks from replication_specs and region_configs blocks to array syntax for MongoDB Atlas advanced clusters. The conversion transforms block-style syntax to list-style syntax and adds validation to ensure required structures are present.

Key changes:

• Converts nested replication_specs blocks to array format
• Converts nested region_configs blocks to array format
• Adds validation for missing replication specs and region configs

Reviewed Changes

Copilot reviewed 14 out of 16 changed files in this pull request and generated 2 comments.

File	Description
internal/convert/adv2v2.go	Core conversion logic with validation for required specs and configs
internal/convert/testdata/adv2v2/*.in.tf	Input test files showing original block syntax
internal/convert/testdata/adv2v2/*.out.tf	Expected output files showing converted array syntax
internal/convert/testdata/adv2v2/errors.json	Error message definitions for validation failures

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[marcosuma]

in all the examples I noticed we don't use num_shards: am I right? I am guessing that's on purpose because you don't still support it but you will?

[marcosuma]

same question applies to the .in.tf examples where there's usage of deprecated fields, such as root disk_size_gb

[lantoli]

correct, the next PR is precisely about removing num_shards and disk_size_gb.

i prefer to do smaller more focused PRs

[EspenAlbert]

Nice! Love that is so little actual logic change! 👏