v2 Rewrite

[mr-karan]

Closes:

• Update on the project status #38
• Log messages should not contain the path of the source files on the build machine #37
• Configuration option server.socket is ignored #36
• Configuration option is undocumented in the README #35
• Build latest docker image #34
• reusing threads on alert updates #25

This is a complete rewrite of calert from scratch.

Improvements: 🚀

• Using koanf which reduces bloat brought in by import dependencies from viper.
• Config is reduced and made simpler
• Support for adding arbitrary providers by making a Provider interface. Currently on Google Chat is supported, plan is to add RocketChat in future.
• Expose Prometheus metrics that show metrics like alerts dispatched, errors etc.
• Basic support for "Threads" in Google Chat to push related alerts in same thread. More details on how this works.
• Automated releases via GitHub Actions.
• Cleaner codebase (Subjective 😉). Something that feels much more nicer to read and maintain compared to previous one.

Deprecation: ⚠️

Various deployment manifests like helm, kustomize, ansible were in this repo. However, I've taken the decision remove them because I don't have any bandwidth to maintain them. If anyone wants, you can still find these manifests in the v1 branch and I plan to keep them archived over there.

Additionally, I'll also be happy to link to external repos dedicated to have these manifests.