limit auto scaling batch size to the size of the training dataset

[awaelchli]

What does this PR do?

Fixes #3259
and releated to #3266

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[codecov]

Codecov Report

Merging #3271 into master will increase coverage by 0%.
The diff coverage is 82%.

@@          Coverage Diff           @@
##           master   #3271   +/-   ##
======================================
  Coverage      90%     90%           
======================================
  Files          98      98           
  Lines        8069    8072    +3     
======================================
+ Hits         7279    7282    +3     
  Misses        790     790           

[mergify]

This pull request is now in conflict... :(

[SkafteNicki]

LGTM

[Borda]

@awaelchli maybe I made a mistake in rebase, mind push your local branch before sync and resolve conflicts...

[mergify]

This pull request is now in conflict... :(

[awaelchli]

@Borda I had to redo all the changes again because the batch size scaling was all moved to a new place and now there appears to be a tuner class? I hope this bugfix can be merged before any further modifications and refactoring are made to the tuner.

[Borda]

LGTM