feat: add check_http_json task for HTTP endpoint assertions with jq

[chetanyb]

Summary

• Add check_http_json task for fetching JSON from HTTP endpoints and evaluating assertions using jq queries
• Support polling, multiple HTTP methods, custom headers/body, and configurable status expectations
• Implement two assertion modes: existence (exists: true/false) and comparison (operator + value)

Test plan

• Unit tests pass with race detector (go test -race)
• Linting clean (golangci-lint run --new-from-rev="origin/master")
• Config validation rejects invalid inputs
• Recursive numeric equality handles nested JSON/YAML type mismatches
• Max 32 jq results enforced per assertion
• Context cancellation stops jq execution

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