multi command support

[colakong]

This patch provides functionality for reading configuration from a yaml file, and supports dispatching alerts to multiple commands based on what match_labels are set in configuration for a command.

Resolves #20
Resolves #21

[otakup0pe]

This all looks fine but to be clear this will be a breaking change as will need to switch to a config file?

[colakong]

This all looks fine but to be clear this will be a breaking change as will need to switch to a config file?

No you don't need to use a config file; It's only loaded if one is defined with the -f flag. You can continue to use prometheus-am-executor the same way as before this change. With this patch, the user can:

• Use it the same way as before, with a command specified at cli
• Use a configuration file, to provide command configuration (supporting dispatch to multiple commands)
• Use both cli-specified command and configuration file. Commands in configuration file that are deemed duplicate entries as a command specified at cli is skipped, so the same command isn't dispatched to twice unless there is some differentiation in terms of matching labels or cli args.