Replace use of old term label with attribute

[MrAlias]

The specification has unified on the term attribute to describe key-value pairs. There exist still many hold-overs of the use of the term label. This updates those uses or deprecates exported types and functions in favor of renamed forms.

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Changed

• The WithLabelEncoder option from the go.opentelemetry.io/otel/exporters/stdout/stdoutmetric package is renamed to WithAttributeEncoder.
• The Batch.Labels field from the go.opentelemetry.io/otel/sdk/metric/metrictest package is renamed to Batch.Attributes.
• The LabelFilterSelector interface from go.opentelemetry.io/otel/sdk/metric/processor/reducer is renamed to AttributeFilterSelector. The method included in the renamed interface also changed from LabelFilterFor to AttributeFilterFor.
• The Metadata.Labels method from the go.opentelemetry.io/otel/sdk/metric/export package is renamed to Metadata.Attributes. Consequentially, the Record type from the same package also has had the embedded method renamed.

Deprecated

• The Iterator.Label method in the go.opentelemetry.io/otel/attribute package is deprecated. Use the equivalent Iterator.Attribute method instead.
• The Iterator.IndexedLabel method in the go.opentelemetry.io/otel/attribute package is deprecated. Use the equivalent Iterator.IndexedAttribute method instead.
• The MergeIterator.Label method in the go.opentelemetry.io/otel/attribute package is deprecated. Use the equivalent MergeIterator.Attribute method instead.

[codecov]

Codecov Report

Merging #2790 (1e4b87b) into main (1884de2) will increase coverage by 0.0%.
The diff coverage is 75.1%.

@@          Coverage Diff          @@
##            main   #2790   +/-   ##
=====================================
  Coverage   75.7%   75.7%           
=====================================
  Files        178     178           
  Lines      11703   11707    +4     
=====================================
+ Hits        8864    8868    +4     
  Misses      2614    2614           
  Partials     225     225           

Impacted Files	Coverage Δ
...rs/otlp/otlpmetric/internal/otlpmetrictest/data.go	0.0% <0.0%> (ø)
...tlp/otlpmetric/internal/otlpmetrictest/otlptest.go	0.0% <0.0%> (ø)
sdk/metric/aggregator/lastvalue/lastvalue.go	87.7% <ø> (ø)
sdk/metric/metrictest/meter.go	100.0% <ø> (ø)
sdk/metric/processor/basic/config.go	100.0% <ø> (ø)
sdk/metric/sdkapi/noop.go	72.7% <0.0%> (ø)
sdk/metric/sdkapi/sdkapi.go	100.0% <ø> (ø)
bridge/opentracing/bridge.go	43.6% <33.3%> (ø)
exporters/stdout/stdoutmetric/config.go	84.3% <50.0%> (ø)
exporters/prometheus/prometheus.go	65.0% <74.0%> (ø)
... and 15 more

[XSAM]

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