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

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

Background

sqlalchemy uses its own EngineTracer and does not capture query parameters
at all today, even though it already uses the semconv stability mechanism.
SQLAlchemy exposes the bound parameters of a statement through its event
system (e.g. the before_cursor_execute hook receives parameters /
executemany).

What to do

• Add a capture_parameters option to the sqlalchemy instrumentor (off by
  default, since parameter values may be sensitive).
• When enabled, emit db.query.parameter.<key> under the new semconv using the
  shared _set_db_query_parameters helper from
  opentelemetry.instrumentation._semconv.
  • Key named parameters (dict) by name and positional parameters (sequence) by
    0-based index.
• Do not capture parameters when SQLAlchemy reports the execution as
  executemany (batch).
• Follow the migration rule: new attribute under the new semconv only. If a
  legacy db.statement.parameters behavior is added for the old semconv, keep
  it behind _report_old; otherwise emitting only the new attribute under the
  new semconv is acceptable since there is nothing to preserve.

Acceptance criteria

• A user can enable parameter capture via capture_parameters.
• New semconv: db.query.parameter.<key> emitted with the correct keys.
• Batch (executemany) executions do not emit db.query.parameter.*.
• Values captured as strings.

Tests

• Cover positional and named parameters, and the batch case.
• Verify exact attribute names and string value types against the spec.
• Test against the oldest and latest supported SQLAlchemy versions.

Start with the SQLAlchemy instrumentor's EngineTracer and its before_cursor_execute event, then read the shared _set_db_query_parameters helper in opentelemetry.instrumentation._semconv. Add coverage for named, positional, and executemany parameters across the oldest and latest supported SQLAlchemy versions. Done means opt-in string-valued db.query.parameter. attributes use correct keys and are absent for batches.