add log level to services

[mdbirnstiehl]

This PR closes #4102.

Added a section to the service.name docs that references the new experience and how to get the most out of the experience, including making sure the log.level is extracted.

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[mdbirnstiehl]

@roshan-elastic could you take a look at this one? Are these changes still relevant?

[roshan-elastic]

Hey @mdbirnstiehl - ah sorry. Yes, this isn't relevant anymore for the moment.

We can cancel this change. Thanks!