Improve docs and migrate to separate website

Usage related changes

Closes #453
Docs are mostly migrated intact from README.md to separate .md files under website/docs/
- Some were improved (e.g. L1-L2 links were dead)
Currently a new website will be deployed for each new push to main
Pending:
- examples section
- documentation versioning

Now the development process also depends on Node/npm
- Updated the executor Docker image in config.yml
Updated contribution guidelines with the content of the # Development section of README.md

[x] Checked out the contribution guidelines
[x] Applied formatting - ./scripts/format.sh
[x] No linter errors - ./scripts/clippy_check.sh
[x] No unused dependencies - ./scripts/check_unused_deps.sh
[x] No spelling errors - ./scripts/check_spelling.sh
[x] Performed code self-review
[x] Rebased to the latest commit of the target branch (or merged it into my branch)
[x] Updated the docs if needed, including the TODO section
[x] Linked the issues resolvable by this PR - linking info
[x] Updated the tests if needed; all passing - execution info