Add structured telemetry fields to ARM API reviewer agent comment marker

[ravimeda]

Updates the hidden HTML marker appended to ARM API reviewer agent comments from
a simple identifier to a structured format with rule ID, severity, and
new/existing classification fields. This enables querying agent-posted comments
by rule, severity, and classification for telemetry purposes.

Updated files:

• .github/agents/arm-api-reviewer.agent.md
• .github/copilot-review-instructions.md

Detection logic in reconciliation scenarios (B and C) updated to use substring
matching for backward compatibility with existing comments.

Marker Format

Each agent-posted comment ends with a hidden HTML marker:

<!-- posted-by: arm-api-reviewer-agent | rule: RPC-Put-V1-11 | severity: blocking | classification: new -->

Telemetry Example

Extract structured telemetry from agent comments on a PR using the gh CLI:

gh api "/repos/Azure/azure-rest-api-specs/pulls/{number}/comments" \
  --jq '[.[] | select(.body | test("posted-by: arm-api-reviewer-agent"))
         | {id, rule: (.body | capture("rule: (?<r>[^ |]+)")).r,
            severity: (.body | capture("severity: (?<s>[^ |]+)")).s,
            classification: (.body | capture("classification: (?<c>[^ ]+)")).c}]'

Sample output:

[
  { "id": 123456, "rule": "RPC-Put-V1-11", "severity": "blocking", "classification": "new" },
  { "id": 123457, "rule": "OAPI027", "severity": "warning", "classification": "existing" }
]

This enables aggregate analysis such as top violated rules, new-vs-existing
issue ratios, and comments-per-PR trends.

[github-actions]

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