ENT-14192: Update parser with event driven cfengine syntax

[victormlg]

Depends on: #6186

This PR simply allows the new event promise type to be parsed, but is ignored by cf-agent. Test policy:

bundle agent main {
  reports:
    "Hello world";
}

body when file_deleted(filename)
{
  files_deleted => { "$(filename)" };
}

bundle agent create_file(filename)
{
  files:
    "$(filename)" create => "true";
}


bundle reactor event_handler {

  events:
    "Create /tmp/a"
      when => file_deleted("/tmp/a"),
      then => create_file("/tmp/a");

    "Create /tmp/b"
      when => file_deleted("/tmp/b"),
      then => create_file("/tmp/b");
}

The syntax here differs from the one defined in the ticket: event promises only take one single when body and one single then bundle. There is a ticket for this in the future.

[larsewi]

LGTM 🚀

[larsewi]

Add a test please :)

[olehermanse]

Fix copyright year, add a minimal syntax test, and wait for release.