Benthos templates should do some linting on config fields for components

[mihaitodor]

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.