bt2: add bt2.get_{greatest_operative,maximal}_mip_version()

Those new functions wrap bt_get_greatest_operative_mip_version() and
bt_get_maximal_mip_version().

bt2.get_greatest_operative_mip_version() excepts a list of
`bt2.ComponentDescriptor` objects. The function builds a component
descriptor set (bt_component_descriptor_set_create()) and adds the
corresponding component descriptors to it and then calls
bt_get_greatest_operative_mip_version().

bt_get_greatest_operative_mip_version() translates
`BT_GET_OPERATIVE_MIP_VERSION_STATUS_NO_MATCH` into `None`.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: Iaeb36b976f3c651fa82a86de2e835f782d682299
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1877
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Simon Marchi <simon.marchi@efficios.com>