move block_ddp_sync_behaviour to utilities

[awaelchli]

What does this PR do?

Moves the context manager block_ddp_sync_behaviour in training loop to utilities. In addition:

• renamed to block_parallel_sync_behavior because it is not ddp specific, applies generally to all parallel plugins
• renamed "behaviour" to "behavior" since majority of our code base and docs uses american english
• renamed the argument "should_block_sync" to just "block" for brevity.
• updated docstring
• made it protected to avoid reviewer commenting that it's public

Part of #9191
Related (but not blocking each other): #9101

Does your PR introduce any breaking changes? If yes, please list them.

While this method was part of the public API, nobody can really effectively use it externally, so we don't consider this a breaking change at all.

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Did you have fun?

I made sure I had fun coding 🙃

[codecov]

Codecov Report

Merging #9192 (b5a7601) into master (f79993a) will increase coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #9192   +/-   ##
======================================
  Coverage      92%     92%           
======================================
  Files         176     176           
  Lines       14860   14861    +1     
======================================
+ Hits        13709   13710    +1     
  Misses       1151    1151           

[tchaton]

Neat !