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/components/SearchImages.tsx

@@ -4,6 +4,7 @@ import { useState } from 'react';
 import Lightbox from 'yet-another-react-lightbox';
 import 'yet-another-react-lightbox/styles.css';
 import { Message } from './ChatWindow';
+import { getServerEnv } from '@/lib/serverEnvironment';
 
 type Image = {
   url: string;
@@ -34,7 +35,7 @@ const SearchImages = ({
             const chatModel = localStorage.getItem('chatModel');
 
             const res = await fetch(
-              `${process.env.NEXT_PUBLIC_API_URL}/images`,
+              `${await getServerEnv("BACKEND_API_URL")}/images`,
               {
                 method: 'POST',
                 headers: {