* feat(service): Adds Mattermost service
* refactor: Removes log msgs
fix: Adds PreSend and PostSend capabilities to user
docs: Updates doc.go and README.md
* refactor: Adds test cases
Adds presend and postsend tests for mattermost service
* refactor: Updates mattermost test cases
* refactor: update mattermost test cases
* refactor: update mattermost hook(s) test cases
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Co-authored-by: EthanEFung <Ethanefung@gmail.com>
Co-authored-by: Niko Köser <koeserniko@gmail.com>