Add emoji tag option to alerts from integrations

In many integrations (e.g., Zabbix, Prometheus), it would be helpful to have emoji that make it easy to see the severity level and type of each alert with emoji.

Following the pattern for the GitHub integration, we should make emoji use a configurable option.

The proposal for how exactly this should look should be posted in the linked thread for feedback, and the message where the plan that received final approval was posted should be linked from the PR. We can do a light-weight audit for which integrations would benefit from this once we've done the first couple.

Related issues / PRs:

• #7177
• #13895
• #37250
• In-progress PR: #31884

CZO thread