docs: add deprecation notes to documentation pages

[tmair]

Description:
This PR adds deprecation notes to the documentation for single method and function overrides. Additionally a strikethrough is also added to the method signature. The source of the changes was the angular.io project, although only the pieces necessary for the deprecations where included.

There are still some places that are a little odd:

• if all function overloads are deprecated, the deprecation note is shown for the function and all of its overloads
• if all function overloads are marked as deprecated the function is not marked with a deprecated badge
• the deprecation notes contain literal links to http://rxjs.dev/... Their purpose is probalby to accomodate IDEs to show the correct link

I am planing on working on some of the issues above in follow up PRs to keep this one simple as I think that this PR already adds value to the documentation.

Examples:
toPromise method

pluck function

publishReplay function

Related issue (if exists):
#5404

[benlesh]

This looks awesome!

cc @niklas-wortmann

[niklas-wortmann]

that's an awesome contribution. Many thanks for that