Fix user-rate-limit alias schema and event fallback (#56328)

* Initial plan

* Fix user rate limit schema aliases and fallback events

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* Clarify user rate limit required field docs

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* Handle missing trigger rate limit fallback

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* Clarify invalid user rate limit log

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* Document rate limit fallback branch

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* Tighten user rate limit alias schema

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* Cover ambiguous user rate limit aliases

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* Note rate limit event list coupling

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* Remove user rate limit legacy aliases

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* Fix user rate limit required docs

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* Test rate limit event list parity

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>