Filter Slackbot crawler

[rcscott]

We get issues reported in Sentry whenever we post our internal app links in Slack because the Slackbot web crawler tries to load them and fails. Would it be possible to get Slackbot added to the list of crawlers that are ignored in Sentry?

[dcramer]

+1

[rcscott]

The three Slack user agents for their crawlers are detailed at https://api.slack.com/robots.

[mattrobenolt]

If we're gonna do this, we might as well also get Facebook and Twitter. Unless we already do. (Not looking at code yet)

[rcscott]

Facebook is in the list of crawlers at https://github.com/getsentry/sentry/blob/master/src/sentry/filters/web_crawlers.py

[mattrobenolt]

Cool, then let's add Slack and Twitter to this. I can do this at some point unless you want to throw up a PR for it. <3

[rcscott]

@mattrobenolt it seemed easy so I went ahead and put up a PR - #5285.