sdk/metrics: copy attributes dict to prevent post-recording mutation (#5106)

* sdk/metrics: copy attributes dict in consume_measurement to prevent mutation

When a caller retains a reference to the attributes dict passed to
counter.add() (or any instrument record/add call), mutating that dict
after the call would silently corrupt the attributes stored on the
aggregation and subsequently on exported data points.

The fix copies the dict at the point where it is first stored as the
canonical attributes for a new aggregation bucket, so downstream
mutations by the caller have no effect.

Fixes #4610

* fix changelog link to point to PR instead of issue

* Apply suggestion from @xrmx

* Create 5106.fixed

* Apply suggestion from @xrmx

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Co-authored-by: tejasae-afk <tejasae-afk@users.noreply.github.com>
Co-authored-by: Mike Goldsmith <goldsmith.mike@gmail.com>
Co-authored-by: Riccardo Magliocchetti <riccardo.magliocchetti@gmail.com>