Python client changes, more docs, fix pdm

[samredai]

Summary

This PR makes a number of minor changes to the python client as well as docs.

• Removed pandas as a requirement for the client and catch+raise when it's not installed (only when the data methods are called). This lets those interested in simply using the CRUD component of the python client to not have to pull in a beefy dependency like pandas.
• Adds a few inspections of the response status and the "state" value to raise some clearer exceptions when the response or query fails.
• Sets engine_name and engine_version defaults to None so the server default is used. I also moved allowed these to be set at client instantiation so users can set it once and have it consistently used through the session. (Users can still override the client setting on individual method calls)
• Adds a client level method for retrieving multiple metrics and dimensions together, dj.data(metrics=[...], dimensions=[...], filters=[...])
• Fills in the content for the "Requesting Data" docs page and makes some corrections to the "Requesting SQL" docs page.

Test Plan

pip installed the client and used it against a local DJ instance.

• PR has an associated issue: #
• make check passes
• make test shows 100% unit test coverage

Deployment Plan

N/A

[shangyian]

LGTM! Left some comments but only one is specifically about this PR

[samredai]

urllib3 broke the world so I'll have to pin to urllib3<2...

[samredai]

Huge thanks to this kind soul for sharing the solution as setting PDM_DEPS='urllib3<2': pdm-project/pdm#1879 (comment)