Use a single http tag to report the server's location to front end, not two

[ashb]

Previously we had both a <base href=""> tag and a <meta name="backend-server-base-url" content=""> tag that contained almost the same
value -- one had a trailing / and the other didn't.

That irked me, so I updated things so the XHR requests take the URL based on
the <base> tag instead.

In order to make this change I made the following changes:

• Instead of erroring if the URL does have a trailing /, the behaviour is
  now to add it if it's missing. This makes it easier kn users
• This necessitated updating the Auth Managers to use a proper URL function,
  not string concatenation, to build the URLs

The change to conf.set is a side-effect/fix to allow conf.set("api", "base_url") to work -- otherwise it errored with "No section found" with only
the defaults present

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[pierrejeambrun]

Let me just try this locally, one moment please :)

[ashb]

@pierrejeambrun Please. It seemed to work find for me in dev and prod modes

[pierrejeambrun]

I am having trouble making it work with a URL prefix, any hint for me ?

Basically setting the base_url to http://localhost:28080/d12345/ (you might need to provide AIRFLOW__API__BASE_URL env variable to breeze too). The front-end should be on http://localhost:28080/d12345/ but there seem to be some routing problem I have a blank page.

If I manually go to the dag page I end up with this:

Let me know if you managed to reproduced or if you want me to take a look. That might just be on my side though.

[pierrejeambrun]

Well, I just tried on main and things do not seem to work anymore either..... :( but the errors are different

[pierrejeambrun]

Nice thanks.

Maybe later we will still want two settings in case the static file are hosted somewhere else (cdn) but for now that's much cleaner.