Add daemonsets

[ekimekim]

Fixes #1444

This adds collection of daemonset info to the probe,
and two new views to the app. One showing only daemonsets,
one showing deployments + daemonsets.

This is too many views (see discussion in #1444), but was useful for initial debugging - we can remove the daemonsets view before merging.

We need to decide how we are going to present this new 'combined view' to the user in a way that makes it obvious what's going on. For now I've labelled it 'Replica groups' but that's not good enough.

[2opremio]

Done with the review: Minor code comment and a fundamental design question.

I don't mind going ahead with this a refining it later, but as a kubernetes user, I find the ReplicaGroup view a bit odd.

[ekimekim]

(addressing design question at the top level instead of at the specific comment)

Yeah, I agree. The view is confusing and right now badly named. Controllers is a better name (though I'm unsure if it's a good name either). I added the daemonset view itself because it was trivial to do and let me ensure it was working correctly.

The ReplicaGroup view was an attempt at addressing concerns in #1444, and yeah I'm looking for ideas on how to make this less confusing.

As I see it, we have three options. In my order of preference:

1. Drop the combined view from this PR and merge it with just the seperate views, as was the original intent of Add view for DaemonSets #1444. We can then work on a better, non-rushed version of the combined view.
2. Merge this PR as-is, with both daemonset view and combined view, and iterate on these issues in a followup.
3. Delay merging this PR (which adds any support for daemonsets at all) until the combined issue is resolved.

[2opremio]

I would go for (1) as well. @rade ?

[rade]

go for (1), but make sure there is a follow up, in particular peeling off bits from #552, specifically replacing (nearly) all existing views with a view that shows you everything in existence, at the highest level of abstraction in which it has a representation.

[ekimekim]

I've removed the combined view parts and otherwise rebased fixups. PTAL.

[2opremio]

Looks good. There is still a comment on a TODO

[ekimekim]

Rebased and resolved conflicts with #2528.
Now propagates errors from getting label selectors for all types, not just daemonsets.
PTAL.

[2opremio]

I am exceptionally merging this myself (and not the PR creator) to move forward with the release