* Amtool: Implement filter by receiver
* Adds receiver flag to amtool alert query
* Adds receiver argument to alert http client
* Updates http client tests for added argument
Also works: scpecifying `receiver: "receiver-123"` in config file
automaticly filters all alerts shown
* Include receiver in amtool config docs
Now that I've implemented the receiver in amtool I should add the new
feature to the documentation.
* #937 Add mention of supporting regex syntax to receiver flag
b949f0dc19