validate manual optimization and supported features before running training

[awaelchli]

What does this PR do?

Provides a better error message for unsupported features with manual optimization.

• gradient clipping (cryptic error message)
• gradient accumulation (would silently not work)

Fixes #7698

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[codecov]

Codecov Report

Merging #7788 (3640220) into master (0b6fd1d) will increase coverage by 4%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #7788    +/-   ##
=======================================
+ Coverage      88%     92%    +4%     
=======================================
  Files         199     199            
  Lines       12987   13016    +29     
=======================================
+ Hits        11412   12014   +602     
+ Misses       1575    1002   -573