[CM] Improve documentation with CM when Filebeat is installed as a service on Windows

[ph]

When a Beat is installed with our service install scripts (install-service-metricbeat.ps1), the script will change the default data path to follow Windows convention.

The new data path will be C:\ProgramData\metricbeat or ``C:\ProgramData\filebeat`. If a user tries to enroll beats without specifying the correct data path, the beat will be enrolled to CM with the wrong UUID and will never receive the configuration.

To fix the problem you can specify at enroll time the new data path using the -path.data option.

Similar to this:

.\metricbeat.exe enroll http://xyz.gov:5601 70f4b584e8024b96b682c46125a8d81a --username elastic --password stdin --force -path.data "C:\ProgramData\metricbeat"

[dedemorton]

@ph I will update the docs, but I'm concerned that users might overlook this. They might copy the command generated by the CM UI and run it without reading the docs at all. Is there any way to add something to the command generated by the U?

BTW, is this a problem on other platforms besides windows?

[ph]

@dedemorton This is a really good point!

We could do one of the following:

1. Add an explicit -path.data on the UI which point to C:\ProgramData\metricbeat
2. Add an explicit -path.data on the UI that point to the current data directory.
3. Search for -path.data in multiple place with the code.

Things I do not want to do is 3, this could open a big can of worms.

I am lacking a information of the Windows deployment usage, @urso or @andrewkroh do you think solution 1 would solve the most cases?

[ph]

@dedemorton Concerning other platforms, this should not be an issue because we install a shim on the platform that takes care of the paths.