CI implementation

Just a quick overview:

1) cspell

The number of distinct unrecognised/misspelled words is 2
------------
doesn
extrafields

There is no much sense in creating separate issues to address those further.
We need to fix "doesn't" and to add "extrafields" to cspell allow a list of the module in this PR (as this is really quick fix to make this step green).

2) The same with phpcs - "Missing short description in doc comment"
This is a one-line and a few-second fix. I think it should be done here as well (with no additional issues).

Thanks!

I have added the CI for the module. To eliminate existing warnings from lints, I have:
1. Included extrafields in _CSPELL_WORDS.
2. Added the phpstan-baseline.neon file to ignore warnings about missing return statements.
3. Corrected some typos in the code.

For now, the lints are functioning well.