doc: add mlflow auth information to docs

[nbowen3]

Relevant issue or PR

Description of changes

In #416, we added a fix so auth for MLFlow properly works. This documents what env need to be set for auth.

Testing done

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 66.87%. Comparing base (2147b14) to head (36ce17a).

❗ There is a different number of reports uploaded between BASE (2147b14) and HEAD (36ce17a). Click for more details.

HEAD has 23 uploads less than BASE

Flag	BASE (2147b14)	HEAD (36ce17a)
	30	7

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #417      +/-   ##
==========================================
- Coverage   76.69%   66.87%   -9.83%     
==========================================
  Files          29       29              
  Lines        3420     3420              
  Branches      533      533              
==========================================
- Hits         2623     2287     -336     
- Misses        565      941     +376     
+ Partials      232      192      -40     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[xalelax]

LGTM!