Benthos templates should do some linting on config fields for components

Currently, setting a non-existent field on a component in a template does not trigger a linter error. For example:

test.tmpl.yaml

name: test
type: input
status: experimental

mapping: |
  #!blobl

  root.generate.count = 0
  root.generate.foobar = "kaboom"
  root.generate.mapping = "root = \"\""

test.yaml

input:
  test: {}
output:
  stdout: {}

$ benthos run --templates ./test.tmpl.yaml test.yaml 

doesn't complain about generate.foobar being an invalid field.

Start by reproducing the issue with test.tmpl.yaml and test.yaml using benthos run --templates ./test.tmpl.yaml test.yaml. Trace how template mappings and component configuration fields are validated; done means an unknown field such as generate.foobar produces a linter error while valid fields continue to work.