docs: extend documentation with keycloak (#5991)

* Update authentication.md

Extend authentication.md with IDP configurations

* Add files via upload

* Delete docs/.gitbook/assets/Keycloak-1.png

* Delete docs/.gitbook/assets/Keycloak-2.png

* Delete docs/.gitbook/assets/Keycloak-4.png

* Delete docs/.gitbook/assets/Keycloak-3.png

* Update docs/deployment/authentication.md

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Co-authored-by: Anthony Powell <apowell@arize.com>