SIP-9: Passkey signature scheme support (#9)

* Add WebAuthn SIP

* add example flows section

* Move SIP-9 into draft status

* Rename SIP-9 assets

* fix typo

* add section about the POC

* remove references to browser wallet and add a note about passkey origin consideration in security section

* Move SIP-9 to Review

* Change SIP-9 status to Stagnant

* Move SIP-9 back to Review status

* update sip-9

* Move SIP-9 to Last Call

* put intent inside hash

* Revert "put intent inside hash"

This reverts commit 52525f8.

* Change SIP-9 status to Final

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Co-authored-by: Will Riches <[email protected]>
Co-authored-by: Joy Wang <[email protected]>