Add release notes for mitaka-1

Create release notes for mitaka-1

Change-Id: If12c87469ddf7d01f901331c569731cd011a71f0

releasenotes/notes/federation-group-ids-mapping-6c56120d65a5cb22.yaml

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+---
+features:
+  - >
+   [`blueprint federation-group-ids-mapped-without-domain-reference <https://blueprints.launchpad.net/keystone/+spec/federation-group-ids-mapped-without-domain-reference>`_]
+   Enhanced the federation mapping engine to allow for group IDs to be
+   referenced without a domain ID.

releasenotes/notes/removed-as-of-mitaka-9ff14f87d0b98e7e.yaml

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+---
+other:
+  - >
+    [`blueprint removed-as-of-mitaka <https://blueprints.launchpad.net/keystone/+spec/removed-as-of-mitaka>`_]
+    Removed ``extras`` from token responses. These fields should not be
+    necessary and a well-defined API makes this field redundant. This was
+    deprecated in the Kilo release.
+  - >
+    [`blueprint removed-as-of-mitaka <https://blueprints.launchpad.net/keystone/+spec/removed-as-of-mitaka>`_]
+    Removed ``RequestBodySizeLimiter`` from keystone middleware. The keystone
+    team suggests using ``oslo_middleware.sizelimit.RequestBodySizeLimiter``
+    instead. This was deprecated in the Kilo release.
+  - >
+    [`blueprint removed-as-of-mitaka <https://blueprints.launchpad.net/keystone/+spec/removed-as-of-mitaka>`_]
+    Notifications with event_type ``identity.created.role_assignment`` and
+    ``identity.deleted.role_assignment`` have been removed. The keystone team
+    suggests listening for ``identity.role_assignment.created`` and
+    ``identity.role_assignment.deleted`` instead. This was deprecated in the
+    Kilo release.
+  - >
+    [`blueprint removed-as-of-mitaka <https://blueprints.launchpad.net/keystone/+spec/removed-as-of-mitaka>`_]
+    Removed ``check_role_for_trust`` from the trust controller, ensure policy
+    files do not refer to this target. This was deprecated in the Kilo
+    release.

releasenotes/notes/x509-auth-df0a229780b8e3ff.yaml

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+features:
+  - >
+   [`blueprint x509-ssl-client-cert-authn <https://blueprints.launchpad.net/keystone/+spec/x509-ssl-client-cert-authn>`_]
+   Support tokenless client SSL x.509 certificate authentication and
+   authorization.