Enable returning full cache with GWDataFindApp.get_cache_data

This MR simplifies the GWDataFindApp.get_cache_data() method to allow retrieving the entire cache, which is required to test the existence of keys in the outermost cache layer (currently <ext>, but probably <obs> in the future).

In practice this allows calls to get_cache_data() with no arguments, while the response to calls with arguments is unchanged.

changed milestone to %GWDataFind Server 1.1.0

added gwdatafind_server.app label

requested review from @duncan.meacher

assigned to @duncan.meacher

added 1 commit

• 16597ae1 - gwdatafind_server.app: simplify get_cache_data

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approved this merge request

mentioned in commit 3ff39184

merged