Adding Username support for non-Config File approach

[aberinnj]

Enhancement PR:

• Adding support for username retrieval from OCI Vault using command line approach
  Though it may no longer be necessary with the config-file approach.

Justification:

• Match azure implementation
• If a simpler deployment using CLI is desired
• If deploying with the DB Operator, without use of config file

[anders-swanson]

lgtm

[anders-swanson]

Config file is the preferred alternative though :)