[👷] Update README in developer-extension to reflect the new build process

[BeltranBulbarellaDD]

Motivation

See Jira.
After migrating the Dev Extension to WXT there are 2 ways to run it. We need to update the docs to reflect that.

Changes

Only developer-extension/README.md

Also edited Dev Extension confluence page. Contribution part

Test instructions

Read README.md

Checklist

• Tested locally
• Tested on staging
• Added unit tests for this change.
• Added e2e/integration tests for this change.
• Updated documentation and/or relevant AGENTS.md file

[cit-pr-commenter-54b7da]

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	168.98 KiB	168.98 KiB	0 B	0.00%	✅
Rum Profiler	4.31 KiB	4.31 KiB	0 B	0.00%	✅
Rum Recorder	24.54 KiB	24.54 KiB	0 B	0.00%	✅
Logs	56.27 KiB	56.27 KiB	0 B	0.00%	✅
Flagging	944 B	944 B	0 B	0.00%	✅
Rum Slim	125.82 KiB	125.82 KiB	0 B	0.00%	✅
Worker	23.63 KiB	23.63 KiB	0 B	0.00%	✅

🚀 CPU Performance

Action Name	Base CPU Time (ms)	Local CPU Time (ms)	𝚫%
RUM - add global context	0.0044	0.0043	-2.27%
RUM - add action	0.0138	0.0139	+0.72%
RUM - add error	0.014	0.0132	-5.71%
RUM - add timing	0.0031	0.0027	-12.90%
RUM - start view	0.0134	0.0127	-5.22%
RUM - start/stop session replay recording	0.0007	0.0007	0.00%
Logs - log message	0.0156	0.0151	-3.21%

🧠 Memory Performance

Action Name	Base Memory Consumption	Local Memory Consumption	𝚫
RUM - add global context	27.34 KiB	28.44 KiB	+1.10 KiB
RUM - add action	102.81 KiB	51.34 KiB	-51.47 KiB
RUM - add timing	26.94 KiB	25.93 KiB	-1.01 KiB
RUM - add error	106.71 KiB	57.28 KiB	-49.43 KiB
RUM - start/stop session replay recording	26.38 KiB	25.82 KiB	-565 B
RUM - start view	471.81 KiB	453.18 KiB	-18.63 KiB
Logs - log message	46.96 KiB	48.09 KiB	+1.13 KiB

🔗 RealWorld