sqlite-utils upsert should require --pk more elegantly

[simonw]

Currently throws an ugly traceback:

% echo '[
            {"id": 1, "name": "Lila"},
            {"id": 1, "name": "Lila"}
        ]' | sqlite-utils upsert data.db chickens -       
Traceback (most recent call last):
  File "/Users/simon/.local/share/virtualenvs/sqlite-utils-C4Ilevlm/bin/sqlite-utils", line 33, in <module>
    sys.exit(load_entry_point('sqlite-utils', 'console_scripts', 'sqlite-utils')())
  File "/Users/simon/.local/share/virtualenvs/sqlite-utils-C4Ilevlm/lib/python3.8/site-packages/click/core.py", line 1137, in __call__
    return self.main(*args, **kwargs)
  File "/Users/simon/.local/share/virtualenvs/sqlite-utils-C4Ilevlm/lib/python3.8/site-packages/click/core.py", line 1062, in main
    rv = self.invoke(ctx)
  File "/Users/simon/.local/share/virtualenvs/sqlite-utils-C4Ilevlm/lib/python3.8/site-packages/click/core.py", line 1668, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/Users/simon/.local/share/virtualenvs/sqlite-utils-C4Ilevlm/lib/python3.8/site-packages/click/core.py", line 1404, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/Users/simon/.local/share/virtualenvs/sqlite-utils-C4Ilevlm/lib/python3.8/site-packages/click/core.py", line 763, in invoke
    return __callback(*args, **kwargs)
  File "/Users/simon/Dropbox/Development/sqlite-utils/sqlite_utils/cli.py", line 1104, in upsert
    insert_upsert_implementation(
  File "/Users/simon/Dropbox/Development/sqlite-utils/sqlite_utils/cli.py", line 906, in insert_upsert_implementation
    db[table].insert_all(
  File "/Users/simon/Dropbox/Development/sqlite-utils/sqlite_utils/db.py", line 2615, in insert_all
    raise PrimaryKeyRequired("upsert() requires a pk")
sqlite_utils.db.PrimaryKeyRequired: upsert() requires a pk

[simonw]

% sqlite-utils upsert trees.db blah -
Usage: sqlite-utils upsert [OPTIONS] PATH TABLE FILE
Try 'sqlite-utils upsert -h' for help.

Error: Missing option '--pk'.