Improve val step logging

[ethanwharris]

What does this PR do?

Fixes #7346

• Changes val step metrics to no longer append /epoch_* to the metric names (which creates many plots in e.g. tensorboard)
• Instead they now store a local step for val and test. Not ideal but this will be changed again in upcoming logger connector refactors (cc @carmocca)
• Refactors log_evaluation_step_metrics to be in the LoggerConnector (where it belongs haha)

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[codecov]

Codecov Report

Merging #7351 (076cda8) into master (2a740eb) will increase coverage by 0%.
The diff coverage is 96%.

@@           Coverage Diff           @@
##           master   #7351    +/-   ##
=======================================
  Coverage      91%     92%            
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  Files         200     200            
  Lines       12925   12991    +66     
=======================================
+ Hits        11801   11904   +103     
+ Misses       1124    1087    -37     

[awaelchli]

Red: master
Blue: this branch

You mention this will change again in a later "refactor". What will change?

[ethanwharris]

@awaelchli I think the functionality will stay the same, only the code will change. The screenshot you show is correct and gives the new behaviour following this PR. Val step logging is and odd usage anyway but at least this stops the potentially hundreds of graphs from being created in tensorboard.

[awaelchli]

Okay, as long as all the other logging for training and epoch end is not affected. Consider changing the labelling here because these per-epoch plots being created was a design decision and therefore expected behaviour.

[awaelchli]

Val step logging is and odd usage anyway

could not agree more 🤣