fix: replace regex in findValOfKey with JSON parsing

[mdryaan]

Description

findValOfKey in tests/e2e/common.go extracted JSON values using a regex ([^,;\\]}]*) that stops at the first comma, semicomp, ], or }. This silently returns truncated data for any JSON value containing those characters — string values with commas are truncated, and nested object values are mangled beyond use.

This replaces the regex with encoding/json unmarshalling and a recursiv key search (searchJSONKey), with jsonValToString for type-safe value serialization back to string.

Related issues

• Fixes findValOfKey regex silently truncates JSON values  #63

How was this tested?

TestFindValOfKey in tests/e2e/common_test.go was added with 5 subtests.

Before the fix, two fail:

After the fix, all 5 pass:

Checklist

• I have read the contribution guide.
• The linter passes locally (make lint).
• The e2e tests of at least one tool pass locally (make test_ctr, make test_nerdctl, make test_docker, make test_crictl).
• If LLMs were used: I have read the llm policy.

[mdryaan]

Hi @cmainas Could you please review this, whenever you get chance.
Thanks