Add e2e test for strategic merge patch

[pmareke]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Add a test sending patches to a ConfigMap API using both json and merge strategies

Which issue(s) this PR fixes:

Fixes #951

Special notes for your reviewer:

Does this PR introduce a user-facing change?

NONE

[linux-foundation-easycla]

• ✅ login: pmareke / name: Pedro López Mareque (2fd1b94, 1da8a68)
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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: pmareke
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