rebrand IRIS -> EarthScope pt. 2

[megies]

What does this PR do?

This is a follow up for #3448 following #3448 (comment)

This changes some more docstring wordings to EarthScope and will show deprecation warnings when using 'IRIS' short URL to initialize an FDSN client and 'iris-federator' when initializing an federator client.

Why was it initiated? Any relevant Issues?

see #3448

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[megies]

I just realized Python is not even showing DeprecationWarnings by default.. what madness is this

Gonna change these warnings to ObsPyDeprecationWarning

[megies]

[megies]

@chad-earthscope did some more changes, will merge this, let me know if there's anything else, but I think this is everything now besides renaming obspy.clients.iris module, which isn't planned as it's to tedious / dangerous to break codes

[chad-earthscope]

Looks good to me, thanks @megies!