HDDS-6853. [Snapshot] Implement Create Snapshot API.

[GeorgeJahad]

What changes were proposed in this pull request?

Added the create snapshot api. It follows the standard ozone ratis request/response model. In addition to saving the metadata for the snapshot to the SnapshotInfoTable, it also creates the checkpoint that corresponds to the snapshot.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-6853

How was this patch tested?

Unit tests here: hadoop-ozone/ozone-manager/src/test/java/org/apache/hadoop/ozone/om/response/snapshot/TestOMSnapshotCreateResponse.java hadoop-ozone/ozone-manager/src/test/java/org/apache/hadoop/ozone/om/request/snapshot/TestOMSnapshotCreateRequest.java hadoop-ozone/common/src/test/java/org/apache/hadoop/ozone/om/helpers/TestOmSnapshotInfo.java