✨ [RUMF-996] set synthetics ids on RUM events

[BenoitZugmeyer]

Motivation

Allow linking RUM to Synthetics tests

Changes

Add Synthetics test id and result id to all RUM events based on global variables. In the future, it will also use cookies, but since we don't know yet how they will be defined, let's do only global variables first.

Testing

Manual, Unit

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I have gone over the contributing documentation.

[codecov-commenter]

Codecov Report

Merging #1007 (90f03b2) into main (fdcb5f9) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1007      +/-   ##
==========================================
+ Coverage   89.04%   89.05%   +0.01%     
==========================================
  Files          86       86              
  Lines        4115     4119       +4     
  Branches      946      946              
==========================================
+ Hits         3664     3668       +4     
  Misses        451      451              

Impacted Files	Coverage Δ
packages/rum-core/src/rawRumEvent.types.ts	100.00% <ø> (ø)
packages/rum-core/src/domain/assembly.ts	98.11% <100.00%> (+0.15%)	⬆️

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[webNeat]

Looking good!