Rename settings from OpenDistro and OpenSearch, with backwards compatibility, using upgraders

[dblock]

Signed-off-by: dblock [email protected]

Description

1. Rename setting from opendistro to opensearch.
2. Provide backwards compatibility for opendistro settings.
3. TODO: tests

Depends on opensearch-project/OpenSearch#643

Manually testing this:

Install OpenDistro

wget https://d3g5vo6xdbdb9a.cloudfront.net/tarball/opendistro-elasticsearch/opendistroforelasticsearch-1.13.2-linux-x64.tar.gz
tar vfxz opendistroforelasticsearch-1.13.2-linux-x64.tar.gz
cd opendistroforelasticsearch-1.13.2
./bin/elasticsearch

Set opendistro.jobscheduler.retry_count: 6.

curl -X PUT "localhost:9200/_cluster/settings?pretty" -H 'Content-Type: application/json' -d'{"persistent":{"opendistro.jobscheduler.retry_count":6}}'

Stop OpenDistro, install OpenSearch on top (or copy data). I built just the minimal engine + job-scheduler from source with these changes.

tar vfxz opensearch-1.0.0-beta1-linux-x64.tar.gz 
cd opensearch-1.0.0-beta1
./bin/opensearch-plugin install opensearch-job-scheduler-1.0.0.0-beta1.zip 
rm -rf data
cp -R ../opendistroforelasticsearch-1.13.2/data .

See it.

[2021-05-04T19:54:40,637][INFO ][o.o.c.s.ClusterSettings  ] [ip-172-31-41-248] updating [opensearch.jobscheduler.retry_count] from [3] to [6]
[2021-05-04T19:54:40,637][INFO ][c.a.o.j.s.JobSweeper     ] [ip-172-31-41-248] Setting background sweep search backoff retry count: 6

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff

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[dblock]

I think upgraders are overkill and we can just use fallback, closing in favor of #20.