Made LogBatchPurger's batch size configurable

[jongpie]

Fixed #807 by adding the ability to declaratively configure the default batch size in LogBatchPurger. This can be used to reduce the batch size to help with mitigating Apex heap size exceptions that can sometimes happen in the LogBatchPurger job when deleting larger volumes of logging data. And making it now configurable makes it easy to quickly change it in orgs as needed.

• Add new LoggerParameter__mdt record LogBatchPurgerDefaultBatchSize
• ℹ️ The new default batch size for LogBatchPurger is now 500 (and now controlled via LogBatchPurgerDefaultBatchSize).
• Previously, 2000 was used, but 500 is the new default to try to help avoid Apex heap size exceptions. If desired, you can update the record's Value__c field to 2000 to restore the previous value/behavior used prior to this release

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.50%. Comparing base (4fbfaa8) to head (1874f49).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #880      +/-   ##
==========================================
+ Coverage   86.19%   91.50%   +5.31%     
==========================================
  Files          17       58      +41     
  Lines        1318     6319    +5001     
  Branches      199      199              
==========================================
+ Hits         1136     5782    +4646     
- Misses        162      517     +355     
  Partials       20       20              

Flag	Coverage Δ
Apex	92.90% <100.00%> (?)
LWC	86.19% <100.00%> (ø)

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