dev: tool/solution for testing various integration key types

[mastercactapus]

Split from #2554

What problem would you like to solve? Please describe:
GoAlert supports multiple systems/inputs for triggering alerts -- it can be difficult for a new contributor/developer to test different functionality from a GoAlert perspective, particularly for systems they may not be familiar with.

• Grafana (esp. with panel images working)
• Prometheus/Alertmanager
• Site24x7
• Email (requires Mailgun, /w public URL and webhooks configured)

Describe the solution you'd like:
A local dev tool that can emulate calls from these different services for testing and general development.

An insomnia collection with a fixed service for testing integration keys is a possible easy-win.

For example, make regendb could create an "Insomnia Test" service auto-favorited with fixed integration keys to simplify testing.

Describe alternatives you've considered:
Manually setting up tools and validating bit-by-bit.

[stale]

This issue has been automatically marked as stale because it has not had recent activity.