[PDOK-16629] validate constraints and indices

[roelarents]

Description

add support for (validating and generating) (unique) indices and foreign keys in table definitions

also a few more pydantic changes after #133

PDOK-16629

Type of change

• New feature
• Improvement of existing feature
• Bugfix
• Refactoring
• Breaking change

Checklist:

• I've double-checked the code in this PR myself
• I've left the code better than before (boy scout rule)
• The code is readable, comments are added that explain hard or non-obvious parts.
• I've expanded/improved the (unit) tests, when applicable
• I've run (unit) tests that prove my solution works
• There's no sensitive information like credentials in my PR