Fix: cpp-common/bt2: make QueryExecutor take ConstValue params

Fix: cpp-common/bt2: make QueryExecutor take ConstValue params

Query executors can take values of any kind, not specifically map
values.  From the doc [1]:

    Unlike the params parameter of the
    bt_graph_add_*_component_*_port_added_listener() functions (see
    Graph), this parameter does not need to be a map value.

Change `ConstMapValue` to `ConstValue`.

[1] https://babeltrace.org/docs/v2.0/libbabeltrace2/group__api-qexec.html#gafb5d324988c2870d66d96c1eeda6f87a

Change-Id: I370182c4aa5df8957c025f59018e359463674156
Reviewed-on: https://review.lttng.org/c/babeltrace/+/12829
CI-Build: Simon Marchi <simon.marchi@efficios.com>
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>