Merge branch 'social_login_hotfixes' into develop

changelog.d/9296.bugfix

changelog.d/9297.feature

changelog.d/9300.feature

changelog.d/9301.feature

changelog.d/9307.misc

changelog.d/9310.doc

docs/sample_config.yaml

synapse/config/sso.py

synapse/handlers/auth.py

synapse/handlers/oidc_handler.py

synapse/handlers/sso.py

synapse/res/templates/sso.css

synapse/res/templates/sso_account_deactivated.html

synapse/res/templates/sso_auth_account_details.html

synapse/res/templates/sso_auth_account_details.js

synapse/res/templates/sso_auth_bad_user.html

synapse/res/templates/sso_auth_confirm.html

synapse/res/templates/sso_auth_success.html

synapse/res/templates/sso_error.html

synapse/res/templates/sso_footer.html