Add "For Developers" guides - Debugging, Encryption and SDP

[mickel8]

Add notes from our the first two internal WebRTC discussions. These include:

• encryption in WebRTC - SRTP, DTLS
• debugging in WebRTC - types of problems, debugging in production, MOS
• SDP - general information, rules, etc.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.82%. Comparing base (38e05e2) to head (944c4cf).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #223      +/-   ##
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+ Coverage   87.79%   87.82%   +0.03%     
==========================================
  Files          54       54              
  Lines        2752     2752              
==========================================
+ Hits         2416     2417       +1     
+ Misses        336      335       -1     

see 1 file with indirect coverage changes

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[Copilot]

Pull Request Overview

A concise set of developer‐focused guides is added to the documentation and registered in the project config.

• Define and include a new for_developers_guides list in mix.exs
• Register the “For Developers” group in extras and sidebar
• Add three markdown guides: SDP, encryption, and debugging

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 11 comments.

File	Description
mix.exs	Added for_developers_guides and integrated into docs config
guides/for_developers/fd_sdp.md	New SDP guide covering general info, rules, and negotiation flows
guides/for_developers/fd_encryption.md	New encryption guide explaining SRTP, DTLS, and key derivation
guides/for_developers/fd_debugging.md	New debugging guide outlining workflow, ICE, DTLS, and QoE