Implemented a landing page for production

[edwinjue]

Hi @bryantran04 @hqasmei

Per Bonnie, I went ahead an implemented a landing page to notify prod site visitors that our site is currently under maintenance. More info can be found in #1441

Please take a look when you have a chance and let me know if there is anything I may have overlooked.

If you want to take a look on localhost, simply checkout this branch by executing from the 311-data project directory:
git checkout --track master-maint

Also, I notice our github actions workflow for frontend prod is a little different and looks like the trigger is a push instead of a pull-request so If I'm not mistaken, an update to the prod site should take place when we git push to master. Is this your understanding as well?

Thanks in advance for taking a look.

Fixes #1441

• Up to date with master branch
• Branch name follows guidelines
• All PR Status checks are successful
• Peer reviewed and approved

Any questions? See the getting started guide

[bryantran04]

LGTM