Rename rds_snapshot to rds_instance_snapshot (ansible-collections#783)

Rename rds_snapshot to rds_instance_snapshot

SUMMARY

Rename rds_snapshot to rds_instance_snapshot since rds_snapshot only handles snapshotting of DB instances. A new module for snapshotting RDS clusters will be added in a future PR.

ISSUE TYPE

New Module Pull Request

COMPONENT NAME

rds_snapshot

Reviewed-by: Mark Chappell <None>
Reviewed-by: None <None>

This commit was initially merged in https://github.com/ansible-collections/community.aws
See: ansible-collections/community.aws@4c44372