Adding ensure UTC default to DB with config option

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When you create a new DB, postgres seems to set the timezone to the host machine by default. This could lead to some odd behavior, especially in development, where your local DB is in PST, but your production DB is in UTC.

Postgres allows you to set this timezone at the session, DB, and global levels. What we could do is add some SQL to set this when you first create your DB:

```crystal
execute <<-SQL
alter database #{Avram::Migrator::Runner.db_name} set time zone '#{Avram.settings.default_timezone}';
SQL
```

By default we could have a habitat setting `default_timezone` that's `UTC`. Then if you wanted to change this, you could. If you inherit a DB, then this would never affect you since you'd never run the create task.

No files or tests are named. Start by locating the database creation task, Avram settings, and the migrator runner; then trace where the database name and default timezone are available. Done means new databases default to UTC, with a configuration option for another timezone, and the behavior is covered by an appropriate test.

Written by the indexing model from the issue text.