Add release notes for Pike

This patch set adds release notes for Pike release.

Change-Id: I4a962ed3d20ca746a470a7ee8b2de2cf703f94f5

releasenotes/notes/action-versioned-notifications-api-ff94fc0f401292d0.yaml

@@ -0,0 +1,3 @@
+---
+features:
+  - Add notifications related to Action object.

releasenotes/notes/audit-tag-vm-metadata-47a3e4468748853c.yaml

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+---
+features:
+  - Added the functionality to filter out instances which have metadata field
+    'optimize' set to False. For now, this is only available for the
+    basic_consolidation strategy (if "check_optimize_metadata" configuration
+    option is enabled).

releasenotes/notes/background-jobs-ha-9d3cf3fe356f4705.yaml

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+---
+features:
+  - Added binding between apscheduler job and Watcher decision engine service.
+    It will allow to provide HA support in the future.

releasenotes/notes/cron-based-continuous-audits-c3eedf28d9752b37.yaml

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+---
+features:
+  - There is new ability to create Watcher continuous audits with cron
+    interval. It means you may use, for example, optional argument
+    '--interval "\*/5 \* \* \* \*"' to launch audit every 5 minutes.
+    These jobs are executed on a best effort basis and therefore, we
+    recommend you to use a minimal cron interval of at least one minute.

releasenotes/notes/gnocchi-watcher-43c25d391fbd3e9c.yaml

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+---
+features:
+  - Added gnocchi support as data source for metrics. Administrator can change
+    data source for each strategy using config file.

releasenotes/notes/jsonschema-validation-79cab05d5295da00.yaml

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+---
+features:
+  - Added using of JSONSchema instead of voluptuous to validate Actions.

releasenotes/notes/noisy-neighbor-strategy-a71342740b59dddc.yaml

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+---
+features:
+  - Added strategy to identify and migrate a Noisy Neighbor - a low priority VM
+    that negatively affects peformance of a high priority VM by over utilizing
+    Last Level Cache.

releasenotes/notes/service-versioned-notifications-api-70367b79a565d900.yaml

@@ -0,0 +1,3 @@
+---
+features:
+  - Add notifications related to Service object.