Fix incorrect article in OtlpJsonLoggingMetricExporter Javadoc

[thswlsqls]

Description

• Fix the indefinite article in the create() Javadoc: "with a aggregation temporality" -> "with an aggregation temporality".
• The sibling create(AggregationTemporality) Javadoc a few lines below already reads correctly; this aligns the two.

Testing done

• Javadoc-only typo, test-exempt: no test added.
• ./gradlew :exporters:logging-otlp:check passed (77 tests).
• No apidiff change and no CHANGELOG entry (not user-facing).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.62%. Comparing base (4d974ba) to head (aff6b43).
⚠️ Report is 42 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #8603      +/-   ##
============================================
+ Coverage     91.55%   91.62%   +0.07%     
- Complexity    10262    10321      +59     
============================================
  Files          1013     1013              
  Lines         27102    27287     +185     
  Branches       3182     3203      +21     
============================================
+ Hits          24812    25001     +189     
+ Misses         1565     1559       -6     
- Partials        725      727       +2     

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