adds render.com url constant

[phishy]

What does this PR do?

adds render.com url constant, similar to the ones for Heroku and Railway

Type of change

• Chore (refactoring code, technical debt, workflow improvements)

How should this be tested?

• ensure app still runs
• deploy to render
• check that public url is same as render dashboard

[vercel]

@phishy is attempting to deploy a commit to the cal Team on Vercel.

A member of the Team first needs to authorize it.