add a resourceCounter to track pods

[tejal29]

Relates to #176

Description
In this PR add a resourceCounter which tracks pods and deployments

• The pods counter is initialized to 0 and used anywhere.

User facing changes

n/a

Next PRs.

• Change getDeployStatus and printResourceStatus to use the resourceCounter.pod
• Fetch pods and add them in the check

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• [ X ] Includes unit tests
• n/a Mentions any output changes.
• n/a Adds documentation as needed: user docs, YAML reference, CLI reference.
• n/a Adds integration tests if needed.

See the contribution guide for more details.

Double check this list of stuff that's easy to miss:

• If you are adding a example to the examples dir, please copy them to integration/examples
• Every new example added in integration/examples dir, should be tested in integration test

Reviewer Notes

• The code flow looks good.
• Unit test added.
• User facing changes look good.

Release Notes

[codecov]

Codecov Report

Merging #3016 into master will increase coverage by 0.16%.
The diff coverage is 84.61%.

Impacted Files	Coverage Δ
pkg/skaffold/deploy/status_check.go	67.44% <84.61%> (+11.68%)	⬆️
pkg/skaffold/runner/timings.go	91.83% <0%> (-0.33%)	⬇️
pkg/skaffold/build/custom/custom.go	62.5% <0%> (ø)	⬆️
pkg/skaffold/schema/v1beta16/upgrade.go	77.77% <0%> (ø)	⬆️
pkg/skaffold/runner/build_deploy.go	67.18% <0%> (ø)	⬆️
pkg/skaffold/runner/dev.go	68.22% <0%> (+0.26%)	⬆️
pkg/skaffold/jib/jib_init.go	89.55% <0%> (+0.66%)	⬆️
pkg/skaffold/build/cluster/sources/sources.go	91.58% <0%> (+0.67%)	⬆️
pkg/skaffold/initializer/init.go	57.19% <0%> (+1.16%)	⬆️

[balopat]

what do you think about moving all these instance methods instead into functions, like the style of append?
func markProcessed(c *counter, err error) counter? that will emphasize it even more that these are not state mutations.