feat: add purge flag to dropTable method

[TylerHillery]

What kind of change does this PR introduce?

Adds the ability to specify if you want purgeRequested set to true or false on the drop table operation.

What is the current behavior?

Currently there is no way to configure the purgeRequested query parameter when dropping a table. The API endpoint supports this parameter to optionally purge the table's data.

What is the new behavior?

Users can now pass an optional options parameter to dropTable() with a purge boolean flag:

// Purge table data (purgeRequested=true)
await catalog.dropTable({ namespace: ['analytics'], name: 'events' }, { purge: true })

// Keep table data (purgeRequested=false, default)
await catalog.dropTable({ namespace: ['analytics'], name: 'events' })

The purge option is mapped to the purgeRequested query parameter expected by the Iceberg REST API. Let me know if we'd prefer to just keep it as the queryParameter.

Additional Context