Add instructions for logs and metrics

[julian-hj]

NOTE: this PR is for the 1.0 release only. Prometheus metrics aren't operational yet in v0.10.0

• Add new "managing" page
• Add a section about fetching logs with kapp
• Add a section about querying metrics with Prometheus

Disclaimer: This may require some format massaging, as I didn't upload it to DocWorks to preview it. I'm happy to pair with a docs person if that's helpful. We might also want to fold the "Rotating credentials" topic under the new "managing" heading, since it's another maintenance task, but I didn't want to make that editorial call.

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[tcdowney]

We might also want to fold the "Rotating credentials" topic under the new "managing" heading, since it's another maintenance task, but I didn't want to make that editorial call.

@emalm @a-peek4 and I are meeting tomorrow to work on a version-agnostic landing page for our docs and discuss some larger reorganization of the topics. I agree it makes sense to fold some of that up under an operator "Managing" or "Administrating ..." page. 👍