refactor: bundle covidcast==0.2.2 in delphi_utils

[dshemetov]

Description

Tried adding a simple wrapper around delphi_epidata.Epidata in here to avoid covidcast, but it grew to become most of the covidcast client from the other repo. So I just bundled the covidcast==0.2.2 in here, which removes transitive dependencies on plotting and geo libaries and unpins Pandas, but also doesn't require us to do any new testing of the client library.

Eventually, we should replace this with epidatpy, but that is possibly months from release.

The main thing we should pay attention to is the Pandas version changing our code behavior (both in client and in indicator pipelines) - we went from pandas-1.5.3 to pandas-2.0.3 (in CI below; not sure why it didn't go up to 2.2.x, pip might just prefer installing a cached version that satisfies the resolver). The unit tests pass below, but it's possible they missed some things. We'll need to look at what behaviors changed from 1.5.3 to 2.0.0. Or we can just pin to 1.5.3 and punt the Pandas bump to another PR.

Changelog

• Moved covidcast.py from here to this repo and brought the test file over as well.
• Updated covidcast imports in this repo.

Fixes

• Partially addresses replace the python covidcast client in validator #1972
• Partially addresses replace the python covidcast client in SirCAL #1931
• Partially addresses replace the python covidcast client in google-symptoms #1987

[melange396]

This is an effective stop-gap for removing the dependency implications of #1972 (and it also partially fulfills #1931 and #1987 ), but it doesnt address the covidcast client inefficiencies mentioned in #1931. It doesnt "replace" the covidcast client as much as it just sources it from a different place...

[dshemetov]

Superseded by #2004