Bug 1719315 - Implement the URL metric type

[brizental]

Pull Request checklist

• Quality: Make sure this PR builds and runs cleanly.
  • Inside the glean/ folder, run:
    • npm run test Runs all tests
    • npm run lint && npm run lint:circular-deps Runs all linters
• Tests: This PR includes thorough tests or an explanation of why it does not
• Changelog: This PR includes a changelog entry to CHANGELOG.md or an explanation of why it does not need one
• Documentation: This PR includes documentation changes, an explanation of why it does not need that or a follow-up bug has been filed to do that work
  • Documentation should be added to The Glean Book when making changes to Glean's user facing API
    • Bug 1719315 - Add documentation about the URL metric type glean#1715

...Also missing:

• glean_parser changes
  • Bug 1719315 - Add support for the URL metric type glean_parser#361
  • https://github.com/mozilla/glean_parser/releases/tag/v3.7.0
• mozilla-pipeline-schemas changes
  • Bug 1719315 - Add the URL metric type to the Glean schema mozilla-services/mozilla-pipeline-schemas#689

Both these changes block this PR, before them the integration tests will not pass.

[brizental]

This is not part of the proposal, but following the same rationale that led us to disallow data: URLs, we should also be disallowing blob: URLs.

[brizental]

Argh, check size fails because of #532

We can retry once that is merged and this is rebased. Or not :)

[badboy]

Looks good.

[moz-glean]

Build size report

Merging #529 into main will:

• Leave the size of full Web Extension bundle unchanged.
• Increase the size of full Qt/QML bundle build by 3%.

---

	Current size	New size	Size increase
Web Extension
core only	45 KB	45 KB	📈 546 bytes
full bundle	69 KB	70 KB	📈 546 bytes
Qt/QML
core only	110 KB	113 KB	📈 3.5 KB
full bundle	110 KB	113 KB	📈 3.5 KB