Don't assume string keys in helm charts

[hugoduncan]

Fixes: #2918
Description

Correctly handle integer keys when replacing values while
deploying Helm charts.

User facing changes

n/a

Before

Panic when helm chart contained integer keys.

After

Integer keys are processed without a panic.

Next PRs.

n/a

Submitter Checklist

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

• Includes unit tests
• Mentions any output changes.
• Adds documentation as needed: user docs, YAML reference, CLI reference.
• 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

• Bug fix
  Correctly handle integer keys when replacing values in helm charts.

[googlebot]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project (if not, look below for help). Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://cla.developers.google.com/ to sign.

Once you've signed (or fixed any issues), please reply here with @googlebot I signed it! and we'll verify it.

---

What to do if you already signed the CLA

Individual signers

• It's possible we don't have your GitHub username or you're using a different email address on your commit. Check your existing CLA data and verify that your email is set on your git commits.

Corporate signers

• Your company has a Point of Contact who decides which employees are authorized to participate. Ask your POC to be added to the group of authorized contributors. If you don't know who your Point of Contact is, direct the Google project maintainer to go/cla#troubleshoot (Public version).
• The email used to register you as an authorized contributor must be the email used for the Git commit. Check your existing CLA data and verify that your email is set on your git commits.
• The email used to register you as an authorized contributor must also be attached to your GitHub account.

ℹ️ Googlers: Go here for more info.

[hugoduncan]

@googlebot I signed it!

[googlebot]

CLAs look good, thanks!

ℹ️ Googlers: Go here for more info.

[codecov]

Codecov Report

Merging #2982 into master will decrease coverage by <.01%.
The diff coverage is 100%.

Impacted Files	Coverage Δ
pkg/skaffold/deploy/kubectl/labels.go	78.57% <100%> (ø)	⬆️
pkg/skaffold/deploy/kubectl/namespaces.go	82.6% <100%> (ø)	⬆️
pkg/skaffold/deploy/kubectl/images.go	92.18% <100%> (ø)	⬆️
pkg/skaffold/deploy/kubectl/matcher.go	100% <100%> (ø)	⬆️
pkg/skaffold/deploy/kubectl/visitor.go	93.75% <100%> (-0.37%)	⬇️