Consolidate Discord notification steps

[HebaruSan]

Motivation

After #4082, I wanted to look for ways to set the first parameter of the Discord notification script (success or failure) without environment variables, extra pseudo-steps ("Set Success"), or side effects. Gradually I realized that writing a git clone command in every place we want to notify was a bit duplicative and could use better encapsulation.

Changes

• Now our own notify.yml action wrapper provides the nice API that DiscordHooks/github-actions-discord-webhook should have.
  • Inputs name and success are accepted, and the DISCORD_WEBHOOK secret is required.
  • The somewhat awkward git clone logic required to use it is now centralized in one place. If the optimal notification method changes in the future, we will be able to update it in just one spot.
• Now what the action documentation calls "ternary operator like behaviour" is used to choose between success and failure based on the value of the boolean success input, with no environment variable twiddling involved.
• Now all spots that previously sent their own notifications are updated to go through the new notify.yml, and the contains expression usees the ! not operator instead of == false.
• The notify jobs in test.yml and smoke.yml now depend on their respective build-* steps to ensure that failure can be detected by checking contains(needs.*.result, 'failure') (if you only needs the intermediate step, its status will be skipped when a previous step fails).

This should be a bit more maintainable, and it gave me some more practice in action coding.

[techman83]

Love this! It was on my hit list to look at 🙂