Auth: Fix US gov azure ad oauth URL parsing

[douglasryanadams]

Updates regex for tenant ID parsing to support .us domains in addition to .com domains for Azure AD.

Fixes #71252

What is this feature?

Allows for Azure AD URLs with domains that end in ".us" in addition to ".com" to support US Gov Azure deployments.

Why do we need this feature?

Fixes a bug that prevents groups using US Gov Azure from integrating Grafana to the [azure.read] Auth scheme.

Who is this feature for?

US Gov Azure organizations.

Which issue(s) does this PR fix?:

Fixes: #71252

Special notes for your reviewer:

Please check that:

• It works as expected from a user's perspective.
• If this is a pre-GA feature, it is behind a feature toggle.
• The docs are updated, and if this is a notable improvement, it's added to our What's New doc.

[CLAassistant]

All committers have signed the CLA.

[Jguer]

Thanks for the fix @douglasryanadams

[douglasryanadams]

Thank you for reviewing and merging this so switftly, it says a lot to us about how well this project is run.

I was able to validate our integration works with this fix today by building from source for Ubuntu. (Confirming that there were no other bugs impeding Gov Azure AD from working at this time, at least for us.)

[Jguer]

Thanks for the kind words, we've identified another detail that has caused us to put in some extra work that is relevant #71365

[grafana-delivery-bot]

The backport to v10.0.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new branch
git switch --create backport-71254-to-v10.0.x origin/v10.0.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x 3a245e49458b4799c105b34807ed8b2a4ebaf192
# When the conflicts are resolved, stage and commit the changes
git add . && git cherry-pick --continue

If you have the GitHub CLI installed:

# Create the PR body template
gh pr view 71254 --json body --template 'Backport 3a245e49458b4799c105b34807ed8b2a4ebaf192 from #71254{{ "\n\n---\n\n" }}{{ index . "body" }}' > .pr-body.txt
# Push the branch to GitHub and a PR
gh pr create --title "[v10.0.x] Auth: Fix US gov azure ad oauth URL parsing" --body-file .pr-body.txt --label "type/bug" --label "area/backend" --label "add to changelog" --label "pr/external" --label "backport" --base v10.0.x --milestone 10.0.x --web

Or, if you don't have the GitHub CLI installed (we recommend you install it!):

# If you don't have the GitHub CLI installed: Push the branch to GitHub and manually create a PR:
git push --set-upstream origin backport-71254-to-v10.0.x
# Remove the local backport branch
git switch main
git branch -D backport-71254-to-v10.0.x

Unless you've used the GitHub CLI above, now create a pull request where the base branch is v10.0.x and the compare/head branch is backport-71254-to-v10.0.x.