WIP - OnConflict support for Insert mutations

[olirice]

What kind of change does this PR introduce?

Adds an "onConflict" argument to insert mutations so they support upsert semantics

• add <Table>Field type for which columns need to update
• add <Table>OnConflictConstraint for which constraint should be used for upsert
• make sure the enum values in <Table>OnConflictConstraint handle camel case and special characters
• update builder restrict_allowed_arguments to dynamically allow an onConflict clause where it exists
• add upsert support to the transpiler
• test happy path
• test no valid constraint exists
• test passing an onConflict object when it isn't supported by the table
• test weird constraint name
• test pkey is serial/generated
• test pkey is user definable

[paulofaria]

I'm really excited about this! @olirice would love to know an ETA for upsert support. Don't feel pressured to answer if for some reason you can't provide an estimation. I know how maintaining OSS is. Keep up the good work, much appreciated! 🙂

[olirice]

I'm hoping to get it knocked out in the next few weeks. Its not too tough of a feature, just need to find some time to go heads down on it

I'm looking forward to using it too!