cmd/ecs - add CLI tool to check if field exists

[andrewkroh]

ecs [field]

ecs is a command-line tool for retrieving definitions of Elastic Common Schema
(ECS) fields. The field definition is written as JSON to stdout.

See https://www.elastic.co/guide/en/ecs/current/ecs-field-reference.html

OPTIONS:

  -h           Show this help message and exit.
  -r           ECS release version (e.g. 8.11.0 or 8.11 or 8).
               Defaults to latest version incorporated into
               github.com/andrewkroh/go-ecs at build time.
  -q           Quiet mode. No ECS definition is written to stdout.

ARGUMENTS:

  field        The name of the ECS field to retrieve the definition for.
               This argument is required.

EXAMPLES:

  ecs source.ip
    Retrieves the JSON definition of the "source.ip" ECS field. 

EXIT STATUS:

   0       Successful completion. Field is defined in ECS.
   1       Field not defined.
   2       Usage/argument problem.