Add a grafana dashboard for boskos resource usage.

[cjwagner]

Questions:

1. The leased and other states were not previously graphed and at a glance they are always 0. Should I remove these from the graphs?
2. I set the default time range to the past day of results. Is that value useful?
3. Do we care what order the graphs are in?
4. Are the colors OK? (I didn't use the automatic colors to ensure that the color schemes are consistent between the graphs.)

Here is what it looks like:

/assign @hongkailiu @stevekuznetsov
/cc @sebastienvas
/area boskos

fixes #15303

[stevekuznetsov]

These are the older metrics -- I would suggest

sum(boskos_resources{type="<my-named-thing>"}) by (state)

[cjwagner]

We don't have that metric in our data... Sounds like our boskos instance isn't being updated properly? I'll open an issue.

[cjwagner]

ref: #11957

[stevekuznetsov]

Whoa. That was added ages ago. I thought boskos was automatically rolled out these days?

[cjwagner]

Boskos is now serving the new metric, the grafana dashboards in this PR have been switched to use that. I also made the graphs stack and fill and tweaked the colors to be more readable. Thanks @michelle192837 for the input!

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[cjwagner]

https://monitoring.prow.k8s.io/d/wSrfvNxWz/boskos-resource-usage?orgId=1