dbtoyaml should allow a user supplied password

[rhunwicks]

dbtoyaml does not allow a password to the database to be passed on the command line, it relies on .pgpass.

We do not allow passwords to be stored in .pgpass because they are stored in clear text.

It would be very helpful if dbtoyaml could prompt the user for a password when one is required, in the same way that psql does.

[jmafc]

Roger, I'll work on this but wanted to point out that an alternative to .pgpass is the environment variable PGPASSWORD. The PG documentation says that also has security concerns, but unfortunately doesn't identify the OSs in question.

[rhunwicks]

I wasn't aware of PGPASSWORD, which will definitely solve the problem
for our use case.