Expose CostmapSubscriber's callback group

[tonynajjar]

My motivation for exposing the callback group as an input is to spin that node independently within a BT node:

(pseudo-code)

  callback_group_ = node_->create_callback_group(
    rclcpp::CallbackGroupType::MutuallyExclusive,
    false);
  callback_group_executor_.add_callback_group(callback_group_, node_->get_node_base_interface());
  costmap_sub_ = std::make_shared<nav2_costmap_2d::CostmapSubscriber>(
    node_, costmap_topic, callback_group_);
  callback_group_executor_.spin_all(bt_loop_duration_);

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
..._2d/include/nav2_costmap_2d/costmap_subscriber.hpp	100.00% <100.00%> (ø)

... and 49 files with indirect coverage changes

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[SteveMacenski]

Would it be reasonable to add that BT node to this PR to add to the Nav2 library? Seems like it might be a general purpose node.

If not, just fix DCO and feel free to merge once done yourself

[tonynajjar]

#5808

The BT node is our version of IsPathValid, so let's discuss in the ticket if we have them merged into one

[SteveMacenski]

Great - we’ll chat there. Fix DCO and feel free to merge once checks pass again.