docs: A few small doc touch-ups in some of the various in_memory_exporter modules

[anarchvile]

Changes

• Fix incorrect "metrics" references in the trace in_memory_exporter docs.
• Fix a broken InMemoryLogExporter doc link.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: anarchvile / name: Lushe Shipkov (dce212f)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.0%. Comparing base (5e29598) to head (dce212f).
Report is 2 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #3042   +/-   ##
=====================================
  Coverage   80.0%   80.0%           
=====================================
  Files        126     126           
  Lines      21879   21879           
=====================================
  Hits       17519   17519           
  Misses      4360    4360           

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