🐛 [RUM] fix retrieving early timings

[bcaudan]

• Add async e2e setup to ensure that early timings are well retrieved
• Add test to ensure that early resources are collected

[codecov-io]

Codecov Report

Merging #268 into master will decrease coverage by 0.07%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #268      +/-   ##
==========================================
- Coverage   86.31%   86.23%   -0.08%     
==========================================
  Files          24       24              
  Lines        1308     1308              
  Branches      277      277              
==========================================
- Hits         1129     1128       -1     
- Misses        179      180       +1

Impacted Files	Coverage Δ
packages/rum/src/rum.entry.ts	71.42% <100%> (ø)	⬆️
packages/logs/src/loggerSession.ts	95.45% <0%> (-4.55%)	⬇️

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