[exporter/debug] format metric data points as one-liners in normal verbosity

[andrzej-stencel]

Description

This pull request is part of #7806; it implements the change for metrics. The changes for logs and traces have been proposed in separate pull requests.

This change applies to the Debug exporter only. The behavior of the Logging exporter remains unchanged. To use this behavior, switch from the deprecated Logging exporter to Debug exporter.

Link to tracking issue

• [exporter/debug] change behavior of "normal" verbosity to be different from "basic" #7806

Testing

Added unit tests for the formatter.

Documentation

Described the formatting in the Debug exporter's README.

[codecov]

Codecov Report

Attention: Patch coverage is 97.82609% with 2 lines in your changes missing coverage. Please review.

Project coverage is 92.49%. Comparing base (3364ba1) to head (66fae40).

Files	Patch %	Lines
exporter/debugexporter/internal/normal/metrics.go	97.70%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10462      +/-   ##
==========================================
+ Coverage   92.46%   92.49%   +0.02%     
==========================================
  Files         390      391       +1     
  Lines       18461    18551      +90     
==========================================
+ Hits        17070    17158      +88     
- Misses       1036     1038       +2     
  Partials      355      355              

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