[Grok Debugger] Do not require mapping to a field name

[ppf2]

This is more of a feature parity request.

In the old grok debugger, if a grok pattern that is not mapped to a field name is used, it will still produce the results grouped under the pattern name, e.g.,

In the Kibana's version of the debugger, it returns nothing as if the pattern cannot match anything:

It will be nice to have the old behavior back.

[bhavyarm]

cc @ycombinator I wasn't sure which team needs to be tagged on this. Thanks!

[ycombinator]

@justinkambic