(#475) Add support for host and process uptime fields

[mdelapenya]

Closes #475

What does this PR do?

This PR adds fields for process.uptime and server.uptime. As suggested by @webmat, the uptime field will be measured in seconds.

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[mdelapenya]

Hey @webmat, I updated the PR to include unit suffix as first-class citizen, so the new fields are
process.uptime.seconds and server.uptime.seconds

cc/ @axw

[webmat]

@mdelapenya Thanks for updating the PR. My suggestion was to make it seconds, but I should have been more explicit: the unit shouldn't be part of the field name. We should have the description state that it's seconds.

In the context of the ecs-metrics experimental branch, we're even considering making this directive official, see #481

[mdelapenya]

Oh my! I understood totally the opposite from the thread :) Also reading how prometheus folks define metrics made me think that way.

Anyway, I'll revert back to the original, where units were explicitly described in fields comments/descriptions

Thanks!

[mdelapenya]

PR updated with your suggestions, thanks!

[webmat]

Thanks for the quick adjustments. I have a few requests still, and then we'll be good.

[webmat]

Sorry I hadn't noticed this. The field set server is meant to describe the server side of a network connection. We have two pairs: client/server and source/destination. As such, this isn't the right place for this.

server.uptime should be moved to host.uptime :-)

Let's also make host.uptime extended for now.

[mdelapenya]

Is extended a matter of adding a level: extended, or is there any other consideration?

[webmat]

Please make this extended for now.

[mdelapenya]

Changes ready!

[webmat]

LGTM

Merge at your convenience :-) No need to backport or anything special.

[mdelapenya]

Thanks @webmat!! What about the docs? Is this something I have to handle too?

[ruflin]

@mdelapenya Docs were generated automatically.

[webmat]

Yes, generated every half hour. But note that master != current on the docs. So you can see your contribution if you go to the docs and select "master" in the version selector.