Create plugin for MatterMost

[bdimitrovski]

As per discussion with @Ma11hewThomas, it would be nice to see this work with Cypress and/or any other other modern testing framework and MatterMost.

Slack and MatterMost are already similar in many aspects, so it would be fairly easy to create a separate plugin only for MM.

I'd be happy to contribute with my knowledge of Cypress/Node/MM etc, as I have so far written something like this in regards to test reporting for MM:

but I'd prefer combining all this information along with the CTRF standard too.

[Ma11hewThomas]

Thanks for the suggestion, the mattermost plugin has now been published here - https://github.com/ctrf-io/mattermost-ctrf

Feel free to propose changes