[Remote Translog] Metadata file naming and its clean up

[gbbafna]

Is your feature request related to a problem? Please describe.

Currently we append timestamp in metadata file name along with primary term and generation . Though we expect that for any given generation and primary term, metadata file will be uploaded only once. Uploading it twice would give IO Exception and would never succeed in first place .

Describe the solution you'd like

Simplication of naming by removing the timestamp from name.

This would make downloads easier , handling duplicate metadata files at upload time and would make deletion of translog metadata files easier.

[ashking94]

@gbbafna I have created issue #6239 for purging up older translog metadata. We can keep this story to be specifically for the naming i.e. removing the timestamp from the metadata file name.