RUM-3669 avoid feature flag spamming events

[xgouchet]

What does this PR do?

This PR attempts to improve the performance linked to setting FeatureFlag evaluations on a RUM View. Namely:

• create an addFeatureFlagBatchEvaluation() method allowing to send a batch of feature flags instead of sending them once at a time. This limits the number of event the Rum View Scope has to process, and the number of view updates written on disk.
• add a check in the RumViewScope handling the feature flags updates: instead of writing an event update for every call to the addFeatureFlagEvaluation() and addFeatureFlagBatchEvaluation() methods, it only writes an event if at least one feature flag value was changed.

Motivation

For some customer updating many feature flags at once, that would result in a lot of RawRumEvents being processed, and a lot of RUM View updates being written on disk. In some extreme cases it could lead to a lot of backpressure on the executor queues.

[codecov-commenter]

Codecov Report

Merging #1932 (8f43597) into release/2.7.0 (9d7e3f9) will decrease coverage by 0.20%.
The diff coverage is 100.00%.

Additional details and impacted files

@@                Coverage Diff                @@
##           release/2.7.0    #1932      +/-   ##
=================================================
- Coverage          83.56%   83.36%   -0.20%     
=================================================
  Files                481      481              
  Lines              17413    17425      +12     
  Branches            2590     2595       +5     
=================================================
- Hits               14550    14526      -24     
- Misses              2177     2186       +9     
- Partials             686      713      +27     

Files	Coverage Δ
.../main/kotlin/com/datadog/android/rum/RumMonitor.kt	28.57% <ø> (ø)
...g/android/rum/internal/domain/scope/RumRawEvent.kt	100.00% <100.00%> (ø)
.../android/rum/internal/domain/scope/RumViewScope.kt	93.47% <100.00%> (-0.48%)	⬇️
.../android/rum/internal/monitor/DatadogRumMonitor.kt	85.35% <100.00%> (+0.09%)	⬆️

... and 18 files with indirect coverage changes

[0xnm]

I'm ok with the change, we just need to define its shape in terms of the pubilc API and align with iOS, I left an idea regarding that.

[ncreated]

Looks good 👍. Minor suggestion on API naming, non-blocking.

[0xnm]

lgtm. regarding the release, I think we will need to release 2.8.0 with buildId support soon (maybe in 2 weeks?), so maybe this change can be shipped there instead of hotfix.