feat: Add MatterMost remote

[JamesMConroy]

Proposed change

Adds a basic mattermost remote to handle receiving webhook events and posting messages with the API.

Should resolve #97

Types of changes

What types of changes is this pull request introducing to flottbot? Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

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• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Testing

To test I used the docker image and add user script from the MM bot example repo https://github.com/mattermost-community/mattermost-bot-sample-golang

[wass3rw3rk]

thanks for the PR and apologies for the delay, i will give it a look in the coming days. also, looking to test it on a real or fake mattermost instance

[JamesMConroy]

No worries @wass3rw3rk stuff happens and I've had PRs sit idle for longer.

This did work with that local mattermost development container, but it didn't work with my company's MatterMost.

We use the version packaged with Gitlab Omnibus and it's a pain to test against because it is in a sandbox environment.

I don't know if it is our configuration or an issue with how I'm using the websocket library, but I would get a panic when trying to connect.

[wass3rw3rk]

I got a local version of Mattermost stood up with Docker and things worked pretty well. A couple of notes below.

Thanks again for the patience.

[JamesMConroy]

@wass3rw3rk Just tested these changes on my work (instance with ssl) and it's working 🎉

[wass3rw3rk]

thanks for testing and tweaks. one more question/suggestion and i think we're good.

[wass3rw3rk]

hey, promise this is the last round from me 😅 might seem like a lot, but most of it is just lower casing log messages to be consistent with the other log messages.

thanks for your patience and fixups!

after those are fixed, we'll run github actions workflows on it and there might be a couple of style tweaks to follow up with 🤞🏼

[JamesMConroy]

@wass3rw3rk no worries, I like making sure things are consistent.

This is the first time I've worked with golangci-lint so I'm sure there are some style issues I've missed.

[wass3rw3rk]

i think this last change should clear out the errors. thanks for the perseverance.

[coveralls]

Pull Request Test Coverage Report for Build 10118959198

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 0.0%

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Totals
Change from base Build 8806816327:	0.0%
Covered Lines:	0
Relevant Lines:	0

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💛 - Coveralls

[wass3rw3rk]

tried this again with local set up and works good! defining insecure as "1" to enable it tripped me up a little. no big deal though as long as we capture in docs.

thanks again (also for the patience)