chore(rfc): add new rfc for the remote feature flags

[rafaeltonholo]

Contribution Summary

Linked Issue/Ticket: Closes #11253

Description

• Add a new RFC for consuming feature flags remotely
• Change RFC 005 state from Proposed to Accepted
• Add RFCs to summary

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• I have read and affirm that my contribution adheres to Mozilla’s Community Participation Guidelines
• This contribution is in Kotlin where possible
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• This contribution includes tests for any new functionality, and maintains tests for any updated functionality.
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• This PR has a descriptive title and body that accurately outlines all changes made, and contains a reference to any issues that it fixes (e.g. Closes #XXX or Fixes #XXX).

[dani-zilla]

I do like this as it'll make the changes we may make to configurations public to anyone who wants to look. It also demystifies it a little. People may think we're using a third party service that could track these changes. Instead, it's just a hosted file they can freely peruse and even change if they want to folk the build and try something different. Of course, there's also local overrides they could use for this.

[dani-zilla]

Thanks for adding this!