feat(microvm): add Terraform compute provider

[edersonbrilhante]

Description

Adds Terraform support for the experimental Lambda MicroVM compute-provider lane on top of #5251 and #5255.

• adds the MicroVM compute-provider and trust-policy modules;
• registers MicroVM in the provider-neutral runner stack;
• adds the minimal multi_runner_config_v2 and webhook schema wiring needed to select MicroVM;
• adds MicroVM routing, validation, IAM, trust-policy, and runner-stack tests;
• adds MicroVM CI matrix entries and MicroVM-specific documentation.

EC2 isolation, common runner-stack refactoring, provider-neutral multi-runner routing, dynamic-label typing, and generic trust-policy wiring are intentionally owned by #5251. This PR has no EC2 subtree changes.

Test Plan

• Commit hooks passed for both commits: Terraform formatting, Terraform validation with TFLint, and merge-conflict checks.
• terraform -chdir=modules/compute-providers/microvm test
• terraform -chdir=modules/compute-providers/microvm/trust-policy test
• terraform -chdir=modules/runner-stack test
• terraform -chdir=modules/multi-runner test
• terraform -chdir=modules/webhook validate
• Verified the 26-file PR diff contains only the MicroVM provider plus required MicroVM schema, registry, test, CI, and documentation wiring.
• Verified the rewritten tip is tree-identical to the previously validated feat(microvm): add Terraform compute provider #5260 tip.
• git diff --check

Related Issues

Depends on #5251 and #5255. Related to #5252.

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None