docs(dotfiles): add hint about using SSH URLs when HTTPS cloning is restricted

[blinkagent]

Some Git providers (e.g. on-prem GitLab) disable HTTPS cloning by default, which causes the dotfiles clone to silently fail during workspace startup. Users see "Startup scripts are still running" but the dotfiles folder is never populated.

This PR adds two small documentation touches:

1. main.tf default description — appends a one-liner suggesting SSH URLs when HTTPS is restricted. This is what users see in the Coder UI parameter prompt.
2. README.md — new "SSH vs HTTPS URLs" section with an example and a brief explanation of why SSH URLs are more reliable during startup.

No logic changes, no new variables — just documentation.

[bjornrobertsson]

Added as Inbound suggestion from customer using a HTTPS URL, which does not utilize the external auth, and/or can cause a silent failure (i.e. .git folder exists, correct reference, but clone will not work while a git:// would)

[github-actions]

Version Bump Required

One or more modules in this PR need their versions updated.

To fix this:

1. Run the version bump script locally:

   ./.github/scripts/version-bump.sh patch

2. Commit the changes:

   git add . && git commit -m "chore: bump module versions (patch)"

3. Push your changes

The CI will automatically re-run once you push the updated versions.

[DevelopmentCats]

After the update for Atif's comment this looks good to me!

But you will need to update the module version in the README @bjornrobertsson