Adding in slack changes for CARTS

[dwhitestratiform]

Description

Current slack notification functionality is noisy and often gives alerts on events we don't particularly care about and omits events that we do care about. This aims to fix that by doing the following.

macpro-mdct-carts-alerts, mdct-prod-releases, and mdct-integrations-channel have all been created in cms slack
webhooks have been requested, created, and populated into github secrets for the SEDS repository
following standards the webhooks were also populated into the carts aws ssm account (readme for this is also updated as part of this PR)
webhooks were implemented to alert on the following things
new pr creation - alerts to the mdct-integrations-channel
failed builds of main, val, or prod - alerts to the macpro-mdct-carts-alerts channel
failed snyk auto merges - alerts to mdct-integrations-channel
release to production - alerts to the mdct-prod-releases channel

Related ticket(s)

https://jiraent.cms.gov/browse/CMDCT-3428

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How to test

merge and watch for issues. this has already been tested in seds.

Notes

once we get all the products done, we'll move everyone over to the new channels but that should be fast after the first one of these goes through and is tested

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Pre-review checklist

• I have performed a self-review of my code
• I have added thorough tests, if necessary
• I have updated relevant documentation, if necessary

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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

[dwhitestratiform]

using branch permissions to merge to integration branch as this is a skip-ci branch it'll never pass all pr checks because no infra is deployed.