Add sentry transactions to covers server

[cdrini]

Closes #8699 . Feature. Let us monitor covers.openlibrary.org performance via sentry.

Technical

• Note I couldn't get it to do the path regex, so it just displays the class name. That's sufficient.
• Corresponding olsystem change: https://github.com/internetarchive/olsystem/pull/199

Testing

• Tested by enabling locally into our sentry, and it worked.
• Patch deployed it to ol-covers and ol-web, and both worked!
• See covers in sentry here: https://sentry.archive.org/organizations/ia-ux/performance/?project=10

Screenshot

Stakeholders

[scottbarnes]

Looks good to me.