Change logging sent to Sentry to provide more meaningful information

[MatousJobanek]

When there is an error (eg. 404 returned from GH) there are two error records sent to Sentry.

1. One for the actual problem:
   logged here: https://github.com/arquillian/ike-prow-plugins/blob/master/pkg/plugin/test-keeper/event_handler.go#L189
   the related issue in the sentry https://errortracking.prod-preview.openshift.io/openshift_io/ike-prow-plugins/issues/5663/

2. And as the error is then returned back, then there is the second record sent to the Sentry from this place: https://github.com/arquillian/ike-prow-plugins/blob/master/pkg/plugin/test-keeper/event_handler.go#L44 (but will be from server.go when this PR is merged). However, this record doesn't provide meaningful information - here is an example of such a sentry issue https://errortracking.prod-preview.openshift.io/openshift_io/ike-prow-plugins/issues/5667/

So, change the logging sent to Sentry so the records/issues provide more meaningful information.

[MatousJobanek]

• The duplicated logging is not necessary - change it so the error is logged only once.
• The logged text shouldn't contain the JSON content (as it is now), but only the cause.

to the fields add:

• link to the issue/PR

• type of the action (updated/created/...)

• content of the comment (in case of the comment event)

• investigate why this issue https://errortracking.prod-preview.openshift.io/openshift_io/ike-prow-plugins/issues/6150/ doesn't contain a reference to the repository

anything else?