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

app.dockerfile

@@ -1,7 +1,7 @@
 FROM node:alpine
 
-ARG NEXT_PUBLIC_WS_URL
-ARG NEXT_PUBLIC_API_URL
+ARG NEXT_PUBLIC_WS_URL='ws://127.0.0.1:3001'
+ARG NEXT_PUBLIC_API_URL='http://127.0.0.1:3001/api'
 ENV NEXT_PUBLIC_WS_URL=${NEXT_PUBLIC_WS_URL}
 ENV NEXT_PUBLIC_API_URL=${NEXT_PUBLIC_API_URL}