[TRNT-4139] Allow serving Trento from a subpath

[antgamdia]

Description

This PR improves the handling of routes and paths when Trento is deployed and served from a subpath, such as foo.example.com/trento.

The rationale is: the reverse proxy adds the usual x-forwarded-prefix to set the subpath where it is being served. Later, TrentoWeb uses this header to calculate the script_name variable that Phoenix uses. The heex templates are updated to honor this variable as well. Finally, some minor tweaks are required on the frontend side, namely: 1) update the base URL in HTTP clients; 2) update some manual redirects (logging in/out) and 3) use relative URLs in some places.

Fixes TRNT-4139

How was this tested?

Unit tests, e2e tests, IRL tests.

Additional information

• Documentation is still pending.
• The suggested NGINX configuration might be affected if using subpaths. See [TRNT-4139] Allow serving Trento from a subpath helm-charts#165

[nelsonkopliku]

Hey @antgamdia, porting here the summary of our private discussion.

While I believe trento would benefit from being able to be exposed in a subpath, I am also not feeling confident it pursuing this path at this very moment.

We'd need to take extra attention about at least the following:

• systemd vs k8s installation
• integration with identity providers
• wanda needs also to be considered
• thorough testing is necessary across different use cases and scenarios

If you ask me, I would defer any commitment on this at this stage 😅