ADP connector: present client mTLS certificates on outbound calls (unblock live execution)

[AtelyPham]

Follow-up to #103 / PR #107.

Problem

The ADP connector ships its manifest + isolation tests only — it cannot execute live. ADP mandates mutual TLS: a client X.509 certificate (CSR-signed by ADP) presented at the TLS handshake on every call, to both:

• the token endpoint accounts.adp.com, and
• the data gateway api.adp.com.

The shared declarative-REST fetch path cannot attach a client certificate to its outbound TLS connection, so every ADP request fails the handshake.

What's needed

• Teach the runtime to present a per-connection client certificate (mTLS) on outbound requests for connectors that require it.
• Wire ADP credentials to carry/reference the client cert + private key (provisioning, storage, rotation).
• Remove the "manifest + tests only" caveat in src/connectors/adapters/adp.ts and enable live execution + integration tests.

References

• Adapter + caveat box: src/connectors/adapters/adp.ts
• Tests (stubbed fetch; mTLS not exercised): tests/adp.test.ts
• Parent epic: tangle-network/agent-dev-container#2268