prometheus: Enable etcd rules

[gracedo]

What type of PR is this?

bug

What this PR does/ why we need it:

When I removed mesosphere-specific etcd rules to use the default, I didn't realize the config here needed to be updated to reflect those changes. I tested adding the rule to the daily cluster and verified all the rules look good.

The change was made in v9.3.4, so we need to backport this to konvoy 1.7/1.6/1.5 (release/3.3, release/3.0, release/2.5)

Also, removed some unnecessary configs that have since been added to the chart values as default (mesosphere/charts#969, https://github.com/mesosphere/charts/pull/962/files#diff-4eefbe60d75fc0250847e2e4dfd675f9977d572e6f0b5615b552b8223719a6caR2324)

Which issue(s) this PR fixes:

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

prometheus(fix): Re-enable etcd prometheus rules

Checklist

• The commit message explains the changes and why are needed.
• The code builds and passes lint/style checks locally.
• The relevant subset of integration tests pass locally.
• The core changes are covered by tests.
• The documentation is updated where needed.

[d2iq-mergebot]

This repo has @mesosphere-mergebot integration. You can perform the following commands by submitting a comment. Submit a comment with content "@mesosphere-mergebot help" to view more detailed help text and examples. Be sure the have a look at the mergebot documentation, too.

@mesosphere-mergebot backport  

[gracedo]

@mesosphere-mergebot backport release/3.3

[gracedo]

@mesosphere-mergebot backport release/3.0

[d2iq-mergebot]

Backport PR for release/3.3: #941

[gracedo]

@mesosphere-mergebot backport release/3.0

[gracedo]

@mesosphere-mergebot backport release/2

[alejandroEsc]

interesting, lgtm.