connections add: Does not support Oracle wallet

[nj1973]

It is possible to configure DVT to use an Oracle wallet for authentication, but the options supported by data-validation connections add Oracle do not cater for it.

To support a wallet I needed to use the url config option which I cannot supply via the command line.

$ cat ~/.config/google-pso-data-validator/ora_local_wallet.connection.json
{"source_type": "Oracle", "url": "oracle+cx_oracle://@system_xepdb"}

There are two potential ways to support Oracle wallet:

1. Enhance by documentation. Simply add a section to the Oracle connections documentation (https://github.com/GoogleCloudPlatform/professional-services-data-validator/blob/develop/docs/connections.md#oracle) detailing that the user must manually create the json file.
2. Enhance DVT to support an option for the connection url. It appears we already support it for DB2.

I propose to attempt option 2 above and if it proves problematic then we can fall back on option 1.

[nj1973]

This issue is related #825