Use larger primary-key field for logger_instance

[jnm]

It's not completely impossible that we'll exceed the maximum capacity of the Postgres integer data type, which is what Django's AutoField uses. Luckily, there's also a BigAutoField—but then there's the perennial question about whether or not we can change the column width in logger_instance without rewriting every row in that huge table.

[jnm]

integer max is 2,147,483,647 per https://www.postgresql.org/docs/14/datatype-numeric.html

[noliveleger]

@jnm FYI: It has been done for logger.Instance and viewer.ParsedInstance
I'm wondering whether or not we should also change InstanceHistory