Use _id instead of osid as field name for auto-generated entity IDs

[gamemaker1]

Most databases/services that auto-add ID fields to entities add it as a _id field. The name osid is confusing and un-intuitive to developers using the registry.

I suggest we use a standard name (e.g., _id) for the field that other services (like MongoDB, ElasticSearch) use already, to make the API more intuitive and easy to get started with for developers.

[pramodkvarma]

Maybe this can be made configuration with default being the current osid. Ensuring backward compatibility to existing large adoptions is key. Let us ensure we don't break upgrades. @dileepbapat any comment on this?

[dileepbapat]

Yeah noted, we will make it configurable and use osid for the cases where compatibility is needed.