User-Agent filter list in the UI / new crawler request

## Summary

Add a setting in the interface to ban bots based on a User-Agent. Or maybe we at least can file the User-Agents so that you could block them manually?

## Motivation

There is a toggle called "Filter out known web crawlers" on the Inbound Filters settings page. Sometimes new crawlers appear that slip by that filter. The bad thing is that ignoring them in `beforeSend` doesn't always work even if a User-Agent is clear. They might be using some kind of cached versions of pages or they might be stripping script objects from pages - in any case, for us the flood of about 200 event per hour hasn't stopped even after adding this code in `beforeSend()`:
```
if (/lyticsbot/.test(window.navigator.userAgent) ||
event.request && event.request.headers && event.request.headers['User-Agent'].search('lyticsbot') !== -1) {
return null;
}
```

## Additional Context

Here is the issue page: https://sentry.io/organizations/policeone/issues/982063112/events/latest/?project=67360 It actually started after upgrading to the new JS SDK (4.6.6) from raven (3.26.4). Prior to that even the `window.navigator.userAgent` was sufficient for blocking errors from that bot.

The crawler's UA in almost 100% of the cases is
```
User-Agent: lyticsbot-external
```