`caller` label

[emschwartz]

Implementations should add a caller label to the function calls counter metric. If you have a function_a that calls function_b and both are instrumented with autometrics, the metrics produced by function_b should have a label {caller="function_a"}.

This makes it easy to look at a specific function's metrics and then very quickly look at the metrics for all of the functions called by that function.

• [x] Rust
• [x] TypeScript https://github.com/autometrics-dev/autometrics-ts/issues/49
• [x] Go
• [x] Python

[flenter]

@emschwartz can you update the list above: Python has support for the caller label.