Add extended database packages to the Rest Agent

[afrancoc2000]

What I'm trying to do

Proposal: I would like to use the Rest Agent with a PostgreSQL database, or any of the databases from the extended repo.

Also the documentation here doesn't match the code.

@troyronda, @fqutishat what do you think?

Expected result

Having the option from the console variables

Actual result

The console variables only allow memory and levelDB

Sample code / test case

aries-agent-rest start -q postgresql -u postgres://YourUserName:YourPassword@YourHostname:5432/YourDatabaseName