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

docker-compose.yaml

@@ -10,17 +10,16 @@ services:
     restart: unless-stopped
 
   perplexica-backend:
-    build:
-      context: .
-      dockerfile: backend.dockerfile
-      args:
-        - SEARXNG_API_URL=http://searxng:8080
+    image: docker.io/andypenno/perplexica-backend:latest
     depends_on:
       - searxng
     ports:
       - 3001:3001
     volumes:
       - backend-dbstore:/home/perplexica/data
+      - ./config.toml:/home/perplexica/config.toml
+    environment:
+      - SEARXNG_API_URL=http://searxng:4000
     extra_hosts:
       - 'host.docker.internal:host-gateway'
     networks:
@@ -28,16 +27,14 @@ services:
     restart: unless-stopped
 
   perplexica-frontend:
-    build:
-      context: .
-      dockerfile: app.dockerfile
-      args:
-        - NEXT_PUBLIC_API_URL=http://127.0.0.1:3001/api
-        - NEXT_PUBLIC_WS_URL=ws://127.0.0.1:3001
+    image: docker.io/andypenno/perplexica-frontend:latest
     depends_on:
       - perplexica-backend
     ports:
       - 3000:3000
+    environment:
+      - BACKEND_API_URL=http://127.0.0.1:3001/api
+      - BACKEND_WS_URL=ws://127.0.0.1:3001
     networks:
       - perplexica-network
     restart: unless-stopped