[RFS] RfsWorker runs through the Snapshot Phase

[chelma]

Description

• Added a new entrypoint, RunRfsWorker.java
• Added a new class RfsWorker to run all the steps in a reindex-from-snapshot operation
• Added a new class OpenSearchCmsClient to handle using the target cluster to coordinate work between the RFS Workers
• Added a state machine for the individual steps of the Snapshot phase
• Added unit tests for the Snapshot phase's steps

Issues Resolved

• https://opensearch.atlassian.net/browse/MIGRATIONS-1691

Testing

• Added unit tests, which pass
• Ran manually using gradle against the local docker-compose setup

chelma@3c22fba4e266 RFS % gradle runRfsWorker --args='--snapshot-name reindex-from-snapshot --s3-repo-uri s3://chelma-iad-rfs-local-testing --s3-region us-east-1 --source-host http://localhost:19200 --target-host http://localhost:29200'

> Task :run
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
14:59:56.127 INFO  Running RfsWorker
14:59:56.129 INFO  Checking if work remains in the Snapshot Phase...
14:59:56.952 INFO  Snapshot not yet completed, entering Snapshot Phase...
14:59:56.952 INFO  Snapshot CMS Entry not found, attempting to create it...
14:59:57.248 INFO  Snapshot CMS Entry created
14:59:57.248 INFO  Attempting to initiate the snapshot...
14:59:58.756 INFO  Snapshot repo registration successful
14:59:59.044 INFO  Snapshot reindex-from-snapshot creation initiated
14:59:59.044 INFO  Snapshot in progress...
14:59:59.324 INFO  Snapshot not finished yet; sleeping for 5 seconds...
15:00:04.397 INFO  Snapshot not finished yet; sleeping for 5 seconds...
15:00:09.477 INFO  Snapshot not finished yet; sleeping for 5 seconds...
15:00:14.557 INFO  Snapshot not finished yet; sleeping for 5 seconds...
15:00:19.687 INFO  Snapshot completed, exiting Snapshot Phase...
15:00:19.687 INFO  Snapshot Phase complete

Check List

• New functionality includes testing
  • All tests pass, including unit test, integration test and doctest
• New functionality has been documented
• Commits are signed per the DCO using --signoff

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[chelma]

This outer while loop is no longer necessary; a holdover from a previous iteration that I forgot to remove.