Validation rules for database names is possibly wrong

[karlskidmore]

Validation rules for database names is possibly wrong (at least for PostgreSQL DBs). Valid names cannot have dashes but can have underscores, but as we can see here:

mu/common/types.go

Line 198 in c0980ac

Name string `yaml:"name,omitempty" validate:"validateLeadingAlphaNumericDash"`

we're specifying the validateLeadingAlphaNumericDash rule, which would allow invalid PostgreSQL database names while prevent use of valid names that used an underscore.