✨ [RUM-4287] Enable feature flags API

[amortemousque]

Motivation

This PR enables sending feature flags with the API introduced in #2096

Changes

Remove the feature_flags experimental flag.

Testing

• Local
• Staging
• Unit
• End to end

---

I have gone over the contributing documentation.

[N-Boutaib]

LGTM

[cit-pr-commenter]

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	157.48 KiB	157.35 KiB	-139 B	-0.09%	✅
Logs	56.12 KiB	56.09 KiB	-32 B	-0.06%	✅
Rum Slim	103.98 KiB	103.84 KiB	-139 B	-0.13%	✅
Worker	25.21 KiB	25.21 KiB	0 B	0.00%	✅

🚀 CPU Performance

Action Name	Base Average Cpu Time (ms)	Local Average Cpu Time (ms)	𝚫
adderror	0.029	0.043	0.013
addaction	0.014	0.018	0.003
logmessage	0.004	0.005	0.000
startview	0.818	0.804	-0.014
startstopsessionreplayrecording	0.709	0.736	0.026
addtiming	0.001	0.001	0.000
addglobalcontext	0.001	0.001	0.000

[bcaudan]

🎉

[bbrzoska]

Looks like the docs need to be updated, as they still say the flag should be added to config.

[BenoitZugmeyer]

Good catch! It's being worked on :) DataDog/documentation#25073 (comment)