[FEATURE] Support creating S3,GCS,Azure Snapshot Repository

[hogesako]

Is your feature request related to a problem?

It seems that only the fs repository is supported in opensearch-java.
https://github.com/opensearch-project/opensearch-java/blob/main/java-client/src/main/java/org/opensearch/client/opensearch/snapshot/RepositorySettings.java

What solution would you like?

It supports S3, GCS, and Azure, just like elasticsearch-java.
https://github.com/elastic/elasticsearch-java/blob/main/java-client/src/main/java/co/elastic/clients/elasticsearch/snapshot/S3RepositorySettings.java
https://github.com/elastic/elasticsearch-java/blob/main/java-client/src/main/java/co/elastic/clients/elasticsearch/snapshot/GcsRepositorySettings.java
https://github.com/elastic/elasticsearch-java/blob/main/java-client/src/main/java/co/elastic/clients/elasticsearch/snapshot/AzureRepositorySettings.java

What alternatives have you considered?

None

Do you have any additional context?

None

[Vaibhav]

+1

[moesterheld]

I would be willing to tackle this, but would need some input how plugin configurations should be handled in the opensearch-api-specification. Can these be added to the spec or should that be avoided?

[moesterheld]

I would be willing to tackle this, but would need some input how plugin configurations should be handled in the opensearch-api-specification. Can these be added to the spec or should that be avoided?

I think I figured it out myself and have added a reference implementation for s3. Once that pr is approved, I will add the other types accordingly.