[tech debt] Stop using ms/BooleanString and only use ms/BooleanValue (#41390)

* [tech debt] Stop using ms/BooleanString and only use ms/BooleanValue

ms/BooleanString will coerce to a string, and we should probably get rid of it and only ever use ms/BooleanValue which will always coerce to a boolean
We want the coercion layer to give us values that are helpful, and true is more helpful than "true".
So we should remove ms/BooleanString and calls to parseBoolean

* Remove ms/BooleanString usage in api/native_query_snippet.clj

* Remove test case related to ms/BooleanString

* Remove the BooleanString schema def as no longer used