Implement ability to assign codes to a site

[m-martinez]

The site table currently only stores the machine-generated name for the site. We should re-purpose this column and allow site coordinators to manually assign a "code" for a site, such as:

apla-hucla “31"
the-hucla “33"

Unfortunately, the name directly maps to LDAP groups which will cause things to fall out of sync. For the time being we should introduce a code column and use this for the URL and reported site codes. This may impact reporting so we should coordinate with data consumers first.

TODO

• [] Add new code column to database and corresponding audit table
• [] Update sqlalchemy models and corresponding API endpoints to expose this field
• [] Add new validated UI field to site modal
• [] Update routing to use site {{code}} instead of {{name}}
• [] Amend unit tests and add new ones