Create RFC to define terraform provider releases & versioning in coder/coder

From standup: https://www.notion.so/coderhq/Week-of-2025-02-17-19dd579be59280e3bfcdf910cf7d3d1e?pvs=4#19dd579be59280228868cd025a5ab37f

1. Versioning in coder/coder
1. Add warnings when used provider version doesn’t match minimum requirements when importing a template version
1. Can we force including a lockfile in template import, to introspect the chosen provider version?
1. What do we do for importing starter templates via the web UI?
2. Could run `terraform init` to end up with the lock file, might require a new provisioner job
3. Ability to update lock-file from UI?
4. Maybe just use the `terraform plan` output, since that includes version
2. Publishing provider releases & testing in dogfood
https://developer.hashicorp.com/terraform/language/expressions/version-constraints#specify-a-pre-release-version

> Terraform does not match pre-release versions on `>`, `>=`, `<`, `<=`, or `~>` operators.

Start with the issue's Terraform version-constraint reference and the listed `terraform init` and `terraform plan` options, then consider provider imports through the web UI and a possible provisioner job. Done means an RFC defines provider release and versioning policy, including minimum-version warnings, lock-file handling, starter-template imports, UI updates, and dogfood testing.

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