[frontier_exploration] update explore boundary dynamically

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Dear all,
I am using frontier_exploration and rtabmap for my robot autonomous exploration.
Now I can send a goal to explore_server without boundary and start to explore.

I notice that the frontier_exploration will set a default boundary
------> the static map (/map) boundary provided by rtabmap package.

But the static map provide by rtabmap will grow when the robot go to new place.
Is there any parameter can be adjust, and let the explore costmap boundary will adjust periodically?