Add Filebeat input plugin

[dmitryilyin]

Add a new Filebeat 6 Monitoring API input plugin.

• Signed CLA.
• Associated README.md updated.
• Has appropriate unit tests.

[gl1ridae]

Hi! Any information regarding when it will be merged?

[Esity]

@gl1ridae what do you think about updating this to work for all beats(filebeat, packetbeat, metricbeat, etc) instead of just filebeat. They should all function pretty similar from a collection and metric perspective and it wouldn't require much for code changes

[gl1ridae]

@Esity Sounds great actually, just checked beats endpoints. I can try to figure it out and create mr.

[dmitryilyin]

@Esity Well, perhaps you're right. I've also made input for kafkabeat #5992 and it's almost identical.

I'll make a single input for "beat" instead.

[nferch]

Since this seemed pretty straightforward, started on merging the two, see nferch@416bb8e . Seems to work with my Filebeat instance, don't have a Kafka instance to test it on.

What do y'all think? @gl1ridae @dmitryilyin

[sjwang90]

Closing this as we'd prefer the general #6653 Beat input plugin. Will re-open if we need to separate them (file, kafka, etc.) out.

Please provide any feedback to PR #6653 and that will help us get it merged in.