Sentry should only activate for supported language files

[ryan-blunden]

Markdown example:

1. Go to https://sourcegraph.com/github.com/sourcegraph/sourcegraph/-/blob/doc/index.md?view=code
   JSON example: It is only necessary to explicitly set the issuer if you are using multiple SAML authentication providers or if no "externalURL" has been set yet, which is also required when you're using a SAML provider.",