Added automatic docker build on merge to master

This PR includes:
- Automatic build & push to docker hub when pushing to master, or when triggering a workflow dispatch on master
- Automatic docker build on pull requests to validate changes
- Updated the docker-compose.yaml to use the container images, rather than building locally
- Added support for defining backend settings using the container environment 
  -> All options defined in config.toml can now be loaded instead from the environment
  -> Order of precedence is environment definition, config.toml, and finally default inline configuration defined in config.ts
- Added support for defining frontend settings using the container environment
  -> Added a dynamic api route to load the container environment definitions on the server, and provide them to the client
  -> Added a library function to fetch from the newly created API, caching the response in the session storage
  -> Modified existing calls to `process.env` to use the new library function
  -> Left the initial statically compiled environment definitions in place as a backup definition, if no environment definitions are provided

Remaining tasks todo before able to merge to [ItzCrazyKns/Perplexica](https://github.com/ItzCrazyKns/Perplexica):
- Add secret definitions for `DOCKER_USERNAME` and `DOCKER_PASSWORD` to [ItzCrazyKns/Perplexica](https://github.com/ItzCrazyKns/Perplexica) to ensure push to dockerhub works on base branch
- Update documentation with information about changes

ui/app/api/env/route.ts

@@ -0,0 +1,16 @@
+import process from 'process';
+import { NextResponse } from 'next/server';
+
+// Enable the Runtime
+export const runtime = "edge"
+
+export async function GET(_request: Request) {
+  // Access environment variables
+  const envVars = {
+    'BACKEND_API_URL': process.env.BACKEND_API_URL ?? process.env.NEXT_PUBLIC_API_URL,
+    'BACKEND_WS_URL': process.env.BACKEND_WS_URL ?? process.env.NEXT_PUBLIC_WS_URL
+  }
+
+  // Return the environment variables as a JSON response
+  return NextResponse.json(envVars);
+}