Fix configuration handling during MergeRollupTask execution

[davecromberge]

Aggregation function parameters and dimensions to erase were being extracted directly from the task configuration without prepending the merge level key.

For example, the task config is encoded by the Task generator as follows:

   "hourly.keyA":  "some value",
   "hourly.keyB": "some other value",
   "mergeLevel": "hourly"

Any lookups on the configuration during task execution have to include the mergeLevel prefix in order to resolve lookups correctly.

There were three options in trying to address this bugfix:

1. Change the encoding of the task config - TaskGenerator would need to strip out the merge level prefix and thus make it easier for key extraction. Problem is that this could break existing functionality.
2. Re-encode all keys without the prefix in the task config. This would bloat the config.
3. Include the merge level prefix in any key lookups - this approach is followed in this PR.

This PR should be tagged with bugfix

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 90.16393% with 6 lines in your changes missing coverage. Please review.

Project coverage is 63.71%. Comparing base (59551e4) to head (6885666).
Report is 1647 commits behind head on master.

Files with missing lines	Patch %	Lines
...on/tasks/mergerollup/MergeRollupTaskGenerator.java	86.11%	4 Missing and 1 partial ⚠️
...minion/tasks/mergerollup/MergeRollupTaskUtils.java	95.65%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #14856      +/-   ##
============================================
+ Coverage     61.75%   63.71%   +1.95%     
- Complexity      207     1484    +1277     
============================================
  Files          2436     2710     +274     
  Lines        133233   151964   +18731     
  Branches      20636    23472    +2836     
============================================
+ Hits          82274    96817   +14543     
- Misses        44911    47879    +2968     
- Partials       6048     7268    +1220     

Flag	Coverage Δ
custom-integration1	100.00% <ø> (+99.99%)	⬆️
integration	100.00% <ø> (+99.99%)	⬆️
integration1	100.00% <ø> (+99.99%)	⬆️
integration2	0.00% <ø> (ø)
java-11	63.68% <90.16%> (+1.97%)	⬆️
java-21	63.60% <90.16%> (+1.97%)	⬆️
skip-bytebuffers-false	63.69% <90.16%> (+1.94%)	⬆️
skip-bytebuffers-true	63.58% <90.16%> (+35.85%)	⬆️
temurin	63.71% <90.16%> (+1.95%)	⬆️
unittests	63.70% <90.16%> (+1.95%)	⬆️
unittests1	56.24% <ø> (+9.35%)	⬆️
unittests2	34.03% <90.16%> (+6.29%)	⬆️

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