Issue with creating duplicated webhooks

1. Create a webhook with name NAME1: `!hookshot webhook NAME1`
2. Create a webhook with name NAME1 again: `!hookshot webhook NAME1`
3. Restart Hookshot.
4. The inbound URL of the webhook becomes the url generated from step 1.

expected result: hookshot webhook inbound URL should stick with the latest one.

Start by reproducing the duplicate `!hookshot webhook NAME1` commands, restarting Hookshot, and tracing the webhook persistence and reload path. Verify that after creating the same-named webhook twice, the inbound URL from the latest creation remains in use after restart.

Written by the indexing model from the issue text.