Support running database scripts as an alternative user

[greatflyingsteve]

When attempting to create the PgSQL database for the BareOS catalog (using the scripts that ship with BareOS), the scripts are always run as the same user that Puppet is running as (root, for most people). This means that root needs password-less access to PgSQL, which for better or worse, most of the PostgreSQL community doesn't seem to treat as normal and PostgreSQL (org) doesn't appear to recommend.

While the init catalog exec isn't written to support an alternative user, Puppet's core exec resource supports using one, and it's quite a lot more common to use the postgres user as the de facto local superadmin for PgSQL. Since there's a breaking-change release in progress already, this would be a good time to add this.

I'll try to file a PR for this later, but if I don't get to it, please don't anybody hesitate to grab this. It should be pretty quick.

[greatflyingsteve]

On further review: there is also no way to tell the module to use a database name other than bareos, which is kinda crazy. For my use case I need to use multiple directors across a huge array of hosts for both US-gov data locality and GDPR compliance requirements, and using the same database name for both is, uh...a significant deviation from best practice at best, and an invitation for accidental data loss at worst.

The module also does not provide any method of setting a database user other than the default bareos user at creation time, nor provide any way of setting a password at creation time for the database user. It also attempts to re-run all of the creation scripts again if certain configuration files are altered, rather than gating the attempt(s) at creation on whether the database already exists, which would make a great deal more sense! If the module is going to attempt to support database creation, these are...kinda bare minimum requirements.

I'm going to update the issue to include at least some of these, as well, and more if I keep finding more things that should be handled.