⚡️ [RUMF-767] start mutation observer only when needed

[amortemousque]

Motivation

Start MutationObserver only when needed for performance optimization

Changes

• start DOM Mutation observation only when we need to track the page activities

Testing

Unit, local

---

I have gone over the contributing documentation.

[codecov-commenter]

Codecov Report

Merging #858 (7f78f66) into main (cbc6064) will decrease coverage by 0.03%.
The diff coverage is 87.50%.

@@            Coverage Diff             @@
##             main     #858      +/-   ##
==========================================
- Coverage   88.62%   88.58%   -0.04%     
==========================================
  Files          80       80              
  Lines        3656     3671      +15     
  Branches      809      812       +3     
==========================================
+ Hits         3240     3252      +12     
- Misses        416      419       +3     

Impacted Files	Coverage Δ
packages/rum-core/src/boot/rum.ts	29.16% <0.00%> (ø)
packages/rum-core/src/domain/lifeCycle.ts	100.00% <ø> (ø)
...ain/rumEventsCollection/action/actionCollection.ts	94.11% <50.00%> (ø)
...ages/rum-core/src/browser/domMutationObservable.ts	87.50% <91.66%> (ø)
packages/core/src/tools/observable.ts	100.00% <100.00%> (ø)
.../domain/rumEventsCollection/action/trackActions.ts	97.87% <100.00%> (ø)
...omain/rumEventsCollection/view/trackViewMetrics.ts	100.00% <100.00%> (ø)
.../src/domain/rumEventsCollection/view/trackViews.ts	97.77% <100.00%> (ø)
.../domain/rumEventsCollection/view/viewCollection.ts	100.00% <100.00%> (ø)
...ackages/rum-core/src/domain/trackPageActivities.ts	100.00% <100.00%> (ø)
... and 1 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update cbc6064...7f78f66. Read the comment docs.