♻️ [RUM-8123] Introduce a hook to assemble events

[amortemousque]

Motivation

Following #3313, reintroduce the hook assemble but keep the contextUrl check in the assembly for now

Changes

• Introduce a Hooks system
• Use the Assemble hook in viewCollection to manage the assembly of view properties
• Use the Assemble hook in urlContext to manage the assembly of url properties

Testing

• Local
• Staging
• Unit
• End to end

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I have gone over the contributing documentation.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.02%. Comparing base (b7fcfcb) to head (cd21fa0).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3330      +/-   ##
==========================================
+ Coverage   92.96%   93.02%   +0.05%     
==========================================
  Files         297      298       +1     
  Lines        7851     7868      +17     
  Branches     1791     1793       +2     
==========================================
+ Hits         7299     7319      +20     
+ Misses        552      549       -3     

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