Allow path prefix multiplexing the dashboard and API

[DL6ER]

What does this implement/fix?

See pi-hole/FTL#2319 for further details. This PR mostly consists of search-and-replace to remove hard-coded absolute paths for the login page as well as adding the ability to send API requests to anywhere else than the fixes /api path.

Note

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

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Related issue or feature (if applicable): Fixes pi-hole/FTL#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.

[XhmikosR]

My only comment in those vars, unsure how to quickly do it better. Have you tried let and disabling any offending ESLint rule for those lines?

[github-actions]

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

[github-actions]

Conflicts have been resolved.

[dschaper]

This is what I'm testing with, and access looks good.

Compose file, running Pi-hole outside of the docker stack on the host:

root@pht:/etc/pihole# cat traefik-pihole-issue-docker.yml 
services:
  traefik:
    image: "traefik:v3.3.3"
    container_name: "traefik"
    command:
      - "--accessLog=true"
      - "--tracing=true"
      - "--api.insecure=true"
      - "--providers.docker=true"
      - "--providers.docker.exposedbydefault=false"
      - "--providers.file.directory=/etc/traefik/"
      - "--entryPoints.web.address=:80"
      - "--entryPoints.dnstcp.address=:53"
      - "--entryPoints.dnsudp.address=:53/udp"
    ports:
      - "53:53"
      - "53:53/udp"
      - "80:80"
      - "8080:8080"
    restart: unless-stopped
    volumes:
      - "/etc/timezone:/etc/timezone:ro"
      - "/var/run/docker.sock:/var/run/docker.sock:ro"
      - "./etc-traefik:/etc/traefik:ro"

  whoami:
    image: "traefik/whoami"
    container_name: "simple-service"
    labels:
      - "traefik.enable=true"
      - "traefik.http.routers.whoami.rule=PathPrefix(`/whoami`)"
      - "traefik.http.routers.whoami.entrypoints=web"
      - "traefik.http.routers.whoami.middlewares=stripwhoami"
      - "traefik.http.middlewares.stripwhoami.stripprefix.prefixes=/whoami/"

Dynamic configuration, file provider, for the host installed Pi-hole.

root@pht:/etc/pihole/etc-traefik# cat dynamic.yaml 
http:
  routers:
    pihole:
      entryPoints:
        - web
      rule: "PathPrefix(`/pihole`)"
      middlewares:
        - piholehttp
      service: piholehttp
  middlewares:
    piholehttp:
      stripPrefix:
        prefixes:
          - "/pihole"
  services:
    piholehttp:
      loadBalancer:
        servers:
          - url: "http://192.168.1.190:8081"

pihole.toml

# Prefix where the web interface is served
# This is useful when you are using a reverse proxy serving the web interface, e.g.,
# at http://<ip>/pihole/admin/ instead of http://<ip>/admin/. In this example, the
# prefix would be "/pihole". Note that the prefix has to be stripped away by the
# reverse proxy, e.g., for traefik:
# - traefik.http.routers.pihole.rule=PathPrefix('/pihole)
# - traefik.http.middlewares.piholehttp.stripprefix.prefixes=/pihole
# The prefix should start with a slash. If you don't use a prefix, leave this field
# empty. Setting this field to an incorrect value may result in the web interface not
# being accessible.
Don't use this setting if you are not using a reverse proxy!

Possible values are:
valid URL prefix or empty
prefix = "/pihole" ### CHANGED, default =