Many project integrations' testing feature is broken

Description

There are a few project services where the testing feature before saving the settings is not working.

This issue is to check which integrations are currently working and to create other issues to fix those that are failing.

Outcomes

[ ] Check the "testing settings" of each integration. [ ] Create a separate issue for each broken integration when doing "testing settings" and add the issue under &5033.

Other things that we can improve along the way:

• Add/update engineering documentation about how to set up each integration.
• Ensure we have any shared login accounts up to date in 1Password.

Integration list (Work-In-Progress):

Key:

• [-] Not working
• Working
• Unknown

Integrations:

• slack
• jira
• slack_slash_commands
• prometheus
• github
• [-] discord #334104 (closed)
• [-] microsoft_teams
• emails_on_push
• pipelines_email
• hangouts_chat
• mattermost
• youtrack
• packagist
• pushover
• jenkins
• redmine
• [-] asana
• teamcity
• external_wiki
• custom_issue_tracker
• drone_ci
• pivotaltracker
• mattermost_slash_commands
• buildkite
• bugzilla
• [-] bamboo
• jenkins_deprecated
• irker
• flowdock
• campfire
• [-] assembla
• unify_circuit
• Webex Teams