fix: using default_scheduler_url as a mounting point for not root path

[franckOL]

(http://address/mount) behind proxy works. fix #3213

Signed-off-by: ROUDET Franck INNOV/IT-S [email protected]

Description

2 files modified to change the build of URL.
api path not at root now, it is in fact the same strategy that use the GUI.

Motivation and Context

Fixes:

• using default_scheduler_url as a mounting point (not root http://address/mount) behind proxy not working #3213
• and https://groups.google.com/g/luigi-user/c/kJ7aI2GNfcE

Have you tested this? If so, how?

I'm able to test:

• With or Without scheduler-url set
• With or Without scheduler-url not at root

[franckOL]

I don't know how to test with tox.
I test locally GUI and API both with mounting point and at root.

[franckOL]

@dlstadther What do you think about that PR ?

[dlstadther]

@franckOL , you'll need to look into and fix any failing tests as a result of this change.

[franckOL]

Not seeing how to fix codeconv. I think my changes are not visible in codecov.
and for failed @github-actions Build / core (3.9, py39-core) (pull_request), Not understanding what happens ! network issue :-)