Towards FUNC-308
## What kind of change does this PR introduce?
Docs update
## What is the current behavior?
Missing error codes definitions for Edge Functions
## What is the new behavior?
This PR adds maps the possible error codes that Edge Functions can
return
<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit
* **Documentation**
* Added a new “Error Codes” guide for Edge Functions, explaining how to
use the `sb-error-code` response header and covering error categories
(bad implementation, authentication, request, server) with causes and
solutions.
* **New Features**
* Updated site navigation to include a direct “Error Codes” link under
the functions menu for quicker access.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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Co-authored-by: Chris Chinchilla <chris@chrischinchilla.com>
