adding additional slack capabilities to mcr

[dwhitestratiform]

Description

Trying to fill in some gaps from the slack implementation this PR does a couple of things

when snyk opens a pr now we alert on failing pr checks, prior we were only alerting on failed deploy/tests from a failed snyk auto merge. This should cover all the failing scenarios for Snyk now.

when a pr is opened the cloudfront URL is added to the slack notification in the integrations channel

I opted not to add alerts in for from red to green builds because it started getting very custom and although nice to have, not a must have.

Related ticket(s)

CMDCT-3534

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How to test

create a pull request and see your cloudfront url in the integrations channel
I tested the failed pr notification in the core repo where we were seeing a failed pr step on a snyk build here

Notes

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Pre-review checklist

• I have added thorough tests, if necessary
• I have updated relevant documentation, if necessary
• I have performed a self-review of my code
• I have manually tested this PR in the deployed cloud environment

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Pre-merge checklist

Review

• Design: This work has been reviewed and approved by design, if necessary
• Product: This work has been reviewed and approved by product owner, if necessary

Security

If either of the following are true, notify the team's ISSO (Information System Security Officer).

• These changes are significant enough to require an update to the SIA.
• These changes are significant enough to require a penetration test.

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convert to a different template: test → val | val → prod

[codeclimate]

Code Climate has analyzed commit 55b7c29 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (90% is the threshold).

This pull request will bring the total coverage in the repository to 95.9% (0.0% change).

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