Support placement_policy resource and database configuration

[otherchen]

Supports creating a placement policy and adding it to a database:

resource "mysql_ti_placement_policy" "test" {
    name = "%s"
    primary_region = "%s"
    regions = %s
    constraints = %s
}

resource "mysql_database" "test" {
    name = "%s"
    default_character_set = "%s"
    default_collation = "%s"
    placement_policy = mysql_ti_placement_policy.test.name
}

[zph]

I found a leftover comment to remove, then looks good to merge and release 👍