`opentelemetry-instrumentation-aiopg`: capture `db.query.parameter.<key>`

Part of #4787 (global db.query.parameter.<key> tracking issue).

Background

aiopg reuses parts of the dbapi machinery but provides its own async
traced_execution in aiopg_integration.py, so it does not inherit the base
parameter-capture logic. It does not capture parameters at all today and does
not expose a capture_parameters option.

What to do

• Add a capture_parameters option to the aiopg instrumentor and thread it
  through to the aiopg integration, mirroring how dbapi / psycopg2 expose it.
• In aiopg's traced_execution, when capture_parameters is enabled:
  • emit db.statement.parameters only under the old semconv;
  • emit db.query.parameter.<key> under the new semconv using the shared
    _set_db_query_parameters helper from
    opentelemetry.instrumentation._semconv.
• Do not capture parameters on batch operations (executemany).
• Reuse the base _populate_span behavior where practical to avoid duplicating
  logic.

Acceptance criteria

• A user can enable parameter capture via capture_parameters.
• Old semconv: only db.statement.parameters.
• New semconv: only db.query.parameter.<key>.
• database/dup: both.
• Values captured as strings; batch operations do not emit
  db.query.parameter.*.

Tests

• Cover old / new / dup modes and the batch case for the async execute paths.
• Verify exact attribute names and string value types against the spec.

Start with the aiopg instrumentor and its custom async traced_execution in aiopg_integration.py, then compare parameter handling in dbapi and psycopg2. Use the shared _set_db_query_parameters helper and cover old, new, dup, and batch modes in the async execute tests. Done means the specified attributes and string values are emitted, with no parameter attributes for executemany.