extend webhook data

[maksim-paskal]

Extend templating instruments for webhook usage:

• Extend templates variables. Read more in README
• Update README with information how to setup Slack
• Raise default webhook timeout to 30s
• Load payload from file (ConfigMap)

BREAKDOWN CHANGES

• removed template {{ .Node }}, now you must use {{ .NodeName }}
• removed template {{ .NewLine }}, if you need new line symbol - load your template from file

Closes: #66

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (a270d83) 98.30% compared to head (0a481c5) 98.53%.

:exclamation: Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #69 +/- ## ========================================== + Coverage 98.30% 98.53% +0.23% ========================================== Files 6 6 Lines 177 205 +28 ========================================== + Hits 174 202 +28 Misses 2 2 Partials 1 1 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.