pcsclient: qeidentity and tdqeidentity are double-encoded as JSON strings in the output JSON

[mythi]

In pcsclient.py _fetch_identity(), the raw HTTP response body (a JSON string) is
assigned directly to the output dict:

    self.output_json["collaterals"][f"{identity_type}identity{key_suffix}"] = identity[0]

When the output dict is serialised with json.dumps(), the string is escaped and
written as a JSON string value instead of a nested object. Consumers reading the
file see e.g.:

"qeidentity": "{\"enclaveIdentity\":{...},\"signature\":\"...\"}"

instead of the expected:

"qeidentity": {"enclaveIdentity": {...}, "signature": "..."}

Fix: parse identity[0] before storing it:

    self.output_json["collaterals"][f"{identity_type}identity{key_suffix}"] = json.loads(identity[0])

The same issue affects tdqeidentity, qveidentity, and their _early variants.
tcbinfos entries are not affected as those are already stored as dicts.