docs: fix ng lint and tools lint command in documentation

[tmair]

Description:
This PR tries to fix the ng lint and the tools lint command of the documentation site (see also #7364 (review)).
It is quite a substantial change, as introducing eslint into the build requires to change also changes in some of the source or tests files.

Related issue (if exists):
This is trying to address the request for fixing ng lint sufaced in PR #7364 (review)

[benlesh]

@jakovljevic-mladen or @niklas-wortmann can you please take a look at this one?

[benlesh]

ping @jakovljevic-mladen or @niklas-wortmann

[niklas-wortmann]

Hey sorry for the delay, I am going to have a look at this after the holidays. Happy holidays everyone

[jakovljevic-mladen]

Hey @tmair, thanks a lot for this PR.

I have left couple of comments that we could address, most of them being related to turning off no-non-null-assertion, but also some other small issues that we could fix.

[tmair]

I rebased the PR against master and addressed the review comments

[tmair]

One more question: Should we add the lint command to the build pipeline or should that be a separate PR once this PR is merged?

[jakovljevic-mladen]

LGTM, thanks a lot again @tmair.

[jakovljevic-mladen]

Should we add the lint command to the build pipeline or should that be a separate PR once this PR is merged?

You can do that in the next PR.