Add detailed error log

[margamraviteja]

Add detailed error log

[mihaitodor]

Simple way to reproduce:

foo.blobl:

map foo {
  root = this.foo | throw("Kaboom!")
}

bar.blobl:

map bar {
  root = this.bar | throw("Kaboom!")
}

benthos.yaml:

input:
  generate:
    count: 2
    mapping: root.map = if count("test") == 1 { "foo" } else { "bar" }
    interval: 0s
  processors:
    - mapping: |
        import "./foo.blobl"
        import "./bar.blobl"
        root = this.apply(this.map)

> benthos -c benthos.yaml
INFO Running main config from specified file       @service=benthos path=benthos.yaml
INFO Listening for HTTP requests at: http://0.0.0.0:4195  @service=benthos
INFO Launching a benthos instance, use CTRL+C to close  @service=benthos
ERRO failed assignment (line 3): failed assignment (line 2): Kaboom!  @service=benthos label="" path=root.input.processors.0
{"map":"foo"}
ERRO failed assignment (line 3): failed assignment (line 2): Kaboom!  @service=benthos label="" path=root.input.processors.0
{"map":"bar"}

Note that the 2 error logs are identical. I think it would help to have apply() inject the map name as an annotation in them.