Refactor/metric exporters non plural

[pitoniak32]

related to comment: #2221 (comment)

Changes

De-pluralize MetricExporter types:

• MetricsExporter{Builder} -> MetricExporter{Builder}
• InMemoryMetricsExporter{Builder} -> InMemoryMetricExporter{Builder}
• PushMetricsExporter -> PushMetricExporter

As I was making these changes I noticed that there is also InMemoryLogsExporter and LogExporter. Will open another PR to address this.

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)

[pitoniak32]

@lalitb - PR that addresses your comment #2241 (comment) about MetricsExporter

[codecov]

Codecov Report

Attention: Patch coverage is 34.88372% with 28 lines in your changes missing coverage. Please review.

Project coverage is 79.4%. Comparing base (afc8ff5) to head (873756f).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
opentelemetry-otlp/src/metric.rs	0.0%	14 Missing ⚠️
opentelemetry-stdout/src/metrics/exporter.rs	0.0%	7 Missing ⚠️
opentelemetry-otlp/src/exporter/http/mod.rs	0.0%	2 Missing ⚠️
opentelemetry-otlp/src/exporter/tonic/mod.rs	0.0%	2 Missing ⚠️
...etry-sdk/src/testing/metrics/in_memory_exporter.rs	71.4%	2 Missing ⚠️
opentelemetry-sdk/src/metrics/mod.rs	87.5%	1 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #2255   +/-   ##
=====================================
  Coverage   79.4%   79.4%           
=====================================
  Files        121     121           
  Lines      20962   20962           
=====================================
  Hits       16656   16656           
  Misses      4306    4306           

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[cijothomas]

LGTM.
We need to consolidate the changelog entries and make a separate migration guide, as there are quite a few changes for the next release.