Allow prefix multiplexing behind reverse proxy

[DL6ER]

What does this implement/fix?

Add new config option webserver.paths.prefix allowing Pi-hole's dashboard and API to be used behind a reverse proxy with path prefix multiplexing. This was already possible in Pi-hole v5.0 without having been added intentionally at any point. It is debatable whether this is a new feature or a bug (because it used to work like this pre-v6.0).

A self-contained docker-compose.yml suitable for testing this can be found in #2298

Note

You will need the related web branch new/web_prefix for this to work as expected.

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Related issue or feature (if applicable): Fixes #2298

Pull request in docs with documentation (if applicable): N/A

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1. I have read and understood the contributors guide, as well as this entire template. I understand which branch to base my commits and Pull Requests against.
2. I have commented my proposed changes within the code.
3. I am willing to help maintain this change if there are issues with it later.
4. It is compatible with the EUPL 1.2 license
5. I have squashed any insignificant commits. (git rebase)

Checklist:

• The code change is tested and works locally.
• I based my code and PRs against the repositories developmental branch.
• I signed off all commits. Pi-hole enforces the DCO for all contributions
• I signed all my commits. Pi-hole requires signatures to verify authorship
• I have read the above and my PR is ready for review.

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[github-actions]

Conflicts have been resolved.

[yubiuser]

Test failed.

[dschaper]

Test failed.

Looks like buildx failures. Triggered a rerun of the failed tests.

[dschaper]

I think the problem is that the builds try to upload debug logs to docker-2 and the debug logs are massive and that causes ansi2html to blow up because it runs gawk on the files and overloads the CPU on docker-2. The ansi2html gets killed and that is seen as a failure?

[yubiuser]

No, they really fail. This PR added a new config option, but the the test were not adjusted.

#9 56.25   1/208 ✗ Compare template and test TOML config files
#9 56.32    (in test file test/test_suite.bats, line 8)
#9 56.32      `[[ "${lines[@]}" == "" ]]' failed
#9 56.32    --- /dev/fd/63
#9 56.32    +++ /dev/fd/62
#9 56.32    @@ -1194,7 +1194,7 @@
#9 56.32       all = true ### CHANGED, default = false
#9 56.32    
#9 56.32     # Configuration statistics:
#9 56.32    -# 154 total entries out of which 97 entries are default
#9 56.32    +# 155 total entries out of which 98 entries are default
#9 56.32     # --> 57 entries are modified
#9 56.32     # 3 entries are forced through environment:
#9 56.32     #   - misc.nice

[DL6ER]

As, yes, sorry. This frequently happens when we merge development which added another seeing as well. git merge things the change to that counter is now already done, it doesn't know if needs to be incremented further now. I'll fix this after work

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[github-actions]

Conflicts have been resolved.

[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/pihole-nginx-not-working/78511/3