Expose fixed model and train kwargs in autotune

[martinkim0]

• Closes Expose model and train kwargs in autotune #2194
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest docs/release_notes/index.md file if fixing a bug or adding a new feature.
• If the changes are patches for a version, I have added the on-merge: backport to x.x.x label.

[codecov]

Codecov Report

Patch coverage: 72.72% and project coverage change: -0.03% ⚠️

Comparison is base (0ee065e) 89.09% compared to head (8f3c66b) 89.07%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2203      +/-   ##
==========================================
- Coverage   89.09%   89.07%   -0.03%     
==========================================
  Files         145      145              
  Lines       11786    11791       +5     
==========================================
+ Hits        10501    10503       +2     
- Misses       1285     1288       +3     

Files Changed	Coverage Δ
scvi/autotune/_tuner.py	100.00% <ø> (ø)
scvi/autotune/_manager.py	81.33% <72.72%> (-0.37%)	⬇️

... and 1 file with indirect coverage changes

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