[Docs] Update gradient/jacobian documentation

[pengmai]

Context: This PR implements some documentation changes that follow up on #244, particularly this comment.

Description of the Change: Update the docstrings for grad and jacobian, rename "defer" to "auto"

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (6b319bd) 99.31% compared to head (8e3db9e) 99.31%.
Report is 1 commits behind head on main.

❗ Current head 8e3db9e differs from pull request most recent head 1cd1103. Consider uploading reports for the commit 1cd1103 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #271   +/-   ##
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  Coverage   99.31%   99.31%           
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  Files          41       41           
  Lines        7131     7131           
  Branches      376      376           
=======================================
  Hits         7082     7082           
  Misses         27       27           
  Partials       22       22           

Files Changed	Coverage Δ
frontend/catalyst/pennylane_extensions.py	99.14% <100.00%> (ø)

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[dime10]

Great, thanks a lot for addressing these :)