Determine desired behavior of logger patternSetter after switching to rapids-logger

[vyasr]

Currently cuml's logger supports setting a pattern in a way that is automatically reset via context management. This approach works because cuml's logger uses a single sink that is defined by cuml itself, and as a result asking for the current pattern via getPattern is well-defined. After the switch to rapids-logger in #6162, that will no longer be the case. The logger will be generalized to support an arbitrary number of sinks (like spdlog itself), meaning that there is no longer a well-defined concept of "the current pattern". While a logger can set a pattern and propagate that to all sinks, it cannot get a single pattern because different sinks could have different patterns set at any given time. As a result, in #6162 I have changed the behavior of the context to reset to the default pattern after the context completes instead of querying for a previous pattern. Once that PR merges we should decide whether that choice is acceptable, whether we want to make a different one, or if we should remove this functionality entirely in favor of a different implementation for the cases that need this sort of context management for logger patterns.