[keyserver] Extend size of hash column for MariaDB cookies table

Summary: In the next diff, we'll be generating a 64-character long hash. This diff makes sure we have space in the MariaDB column for it.

Test Plan:

1. Make sure existing cookies still work by refreshing the web app in my local environment
2. Create a new cookie by logging out and back in on web in my local environment. Refresh the page to make sure things still work

Reviewers: atul, tomek

Reviewed By: tomek

Subscribers: wyilio

Differential Revision: https://phab.comm.dev/D9547