MSC4133: Extending User Profile API with Key:Value Pairs (#4133)

* Extended profile fields

* Unstable client features

* Clarification on limits

* Warning about avatar_url and displayname limits

* Error code clarification

* Whitespace fixes

* Adjusted size limits

* Clarified Canonical JSON

* Clarifications

* Clarifications

* Remove UTF-16

* Clarify key persistence

* Out of date line

* Clarify only `u.*` namespace is limited to 512 bytes

* Include read-only fields in capability

* Change missing capability behaviour

* Typo correction

* Privacy clarification for T&S

* Consolidation and rewrite

* Whitespace fix

* Safety and security updates

* Clarify servers can hide fields

* References to MSC4201 and MSC4202

* Clarify redacted `m.room.member` events

* Error codes and redundant instructions

* Removing custom fields

* Typo fix

* Clarifications and readability

* Correct key length error to match common grammar limit

* Remove PATCH/PUT.

* Removed redundant sections after `PUT` and `PATCH` methods removed

* Re-add client feature for managing profile fields

* Update proposals/4133-extended-profiles.md

Co-authored-by: Travis Ralston <[email protected]>

* Clarify 403 error scenarios

* Add section on caching behaviour under S-S API

* Link to Canonical JSON in current spec

* Cut down instructions for clients on when to display content from federated users.

* Revert c82dab6

* Clarify caching and freshness challenges

* Adjust abuse section

* Authentication/rate-limiting/guest access requirements

* Un-revert accidental revert of af87bbe

* Simplify caching recommendations

* Up to clients whether they check capability

Co-authored-by: Richard van der Hoff <[email protected]>

* Technically correct is the best kind of correct

Co-authored-by: Richard van der Hoff <[email protected]>

* Link to current federation profile endpoint

Co-authored-by: Richard van der Hoff <[email protected]>

* Mention check for spec version when using profile fields

Co-authored-by: Richard van der Hoff <[email protected]>

* Attempt to clarify what servers should not enforce about key naming

* Fix line wrapping after 9b2918e

* Add `M_MISSING_PARAM` error

* Clarify where errors apply

* Clarify optional ability to not always federate every field

* Fix inconsistent line wrapping

* Offer suggestions for hiding extended fields when member event redacted

Co-authored-by: Andrew Morgan <[email protected]>

* Fix wrapping length of one line

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Co-authored-by: Patrick Cloke <[email protected]>
Co-authored-by: Travis Ralston <[email protected]>
Co-authored-by: Richard van der Hoff <[email protected]>
Co-authored-by: Andrew Morgan <[email protected]>