feat(schema): allow custom constraint names

[graduenz]

Context

Right now, we have a hardcoded constraint format for primary keys:

sb.QuoteIdentifier("PK_" + pTable.Name())

That means, for a said users table, it will always be PK_users, which is fine, but users can't change this pattern if they want, and they might want to go with other formats:

• users_PK (suffix instead of prefix)
• pk_users (lowercase)
• any other format

Requirements

Ideally, we should allow doing both:

• Set up a custom format for constraint types (for primary keys, for foreign keys, etc.)
• or, define exact names for constraints (bypassing the format)

Important

Don't work on this issue before this other issue is done, which will introduce more constraint types.