Add on_predict_{batch,epoch}_{start,end} and Callback.on_predict_{start,end}

[carmocca]

What does this PR do?

Split out from #7042 and #7127

Notes:

• self.log is not allowed in the predict hooks

cc: @justusschock @tchaton

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[codecov]

Codecov Report

Merging #7141 (43a5475) into master (1477520) will decrease coverage by 6%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #7141    +/-   ##
=======================================
- Coverage      92%     86%    -6%     
=======================================
  Files         197     197            
  Lines       12662   12796   +134     
=======================================
- Hits        11674   11059   -615     
- Misses        988    1737   +749     

[tchaton]

LGTM !
Need to add the calls on trainer callbacks too for the new ones.

[tchaton]

LGTM ! Thanks.