Issue 212/extensions

[rphovley]

The Pull Request is ready

• [x] all github actions are passing
• [x] are changes backwards compatible?
• [x] fixes #212
• [x] the branch follows the naming schema issue-123-enable-x-does-not-disable-y
• [x] the pull request has a sensible title

Intention

With this change I intend to add the extension marketplace. Includes the sql sandbox extension as an example. Included documentation for others to add their own extensions

Review Points

Please take extra care reviewing...

The code follows best practices

• [x] the code is readable
• [x] issues for follow-up tasks have been created
• [x] there is no any type used

Notes

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit b436f13):

https://codeclimbersio--pr231-issue-212-extensions-rjloptsd.web.app

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