GEP 1767: CORS Filter (#3435)

* GEP 1767: CORS Filter

* GEP 1767: CORS Filter

* Apply suggestions from code review

CORS GEP updates based on the review comments.

Co-authored-by: Mattia Lavacca <[email protected]>

* GEP 1767: apply suggestions from code review about GEP status.

* Apply suggestions from code review about AllowOrigins and AllowMethods

Co-authored-by: Nick Young <[email protected]>

* GEP 1767: CORS Filter

* GEP 1767: CORS Filter

* Apply suggestions from code review

CORS GEP updates based on the review comments.

Co-authored-by: Mattia Lavacca <[email protected]>

* GEP 1767: apply suggestions from code review about GEP status.

* GEP 1767: apply suggestions from code review about GEP status.

* GEP-1767: alternatives considered

* GEP-1767: alternatives considered

* GEP-1767: alternatives considered

* GEP-1767: add a string enumerated field for config AllowCredentials

* GEP-1767: the config AllowMethods and AllowHeaders are not optional

* GEP-1767: use HTTPMethod as type of config AllowMethods

* GEP-1767: add cross-origin examples before API section

* GEP-1767: format string

* GEP-1767: setting a default header Access-Control-Max-Age: 5 when the field MaxAge is unspecified

* GEP-1767: set status topProvisional

* GEP-1767: multiple names in the value of the response header Access-Control-Allow-Methods, Access-Control-Allow-Headers and Access-Control-Expose-Headers are separated by a comma

* GEP-1767: updates about * wildcard for the request with include credentials

* GEP-1767: updates about response header of Access-Control-Allow-Methods, Access-Control-Allow-Headers and Access-Control-Expose-Headers

* GEP-1767: updates about AllowOrigins field

* GEP-1767: format Introduction

* GEP-1767: updates about format

* GEP-1767: fix error case about field AllowHeaders

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Co-authored-by: Mattia Lavacca <[email protected]>
Co-authored-by: Nick Young <[email protected]>