[Remote Segment Store] Define RemoteDirectory interface

[sachinpkale]

Is your feature request related to a problem? Please describe.
As described in the Feature Proposal, all the read/write operations to remote segment store will happen via RemoteDirectory interface. This task will define the RemoteDirectory interface along with corresponding RemoteIndexInput (extends IndexInput) and RemoteIndexOutput (extends IndexOutput) classes.

Describe the solution you'd like
ToDo

Describe alternatives you've considered
ToDo

Additional context
ToDo

[sachinpkale]

Initial implementation can be found in the fork: https://github.com/sachinpkale/OpenSearch/blob/feature/remote_directory/server/src/main/java/org/opensearch/index/engine/RemoteDirectory.java

Corresponding RemoteIndexInput and RemoteIndexOutput.

Next steps:

1. Move these files to correct package structure, should be under org.opensearch.index.store
2. Add javadoc/comments - for Directory methods that will not be supported in RemoteDirectory in V1, we need to explicitly add comments on why it is not supported.
3. Add unit tests.
4. Raise PR to merge to main

[sachinpkale]

Moved RemoteDirectory file under new package: org.opensearch.index.store and added javadoc/comments.

1. RemoteDirectory
2. RemoteIndexInput
3. RemoteIndexOutput

Next step: Add unit tests and raise PR.

[sachinpkale]

PR link: #3102