Validate timeseries data using explicit value and rtol

[danielhuppmann]

Please confirm that this PR has done the following:

• Tests Added
• Documentation Added
• Name of contributors Added to AUTHORS.rst
• Description in RELEASE_NOTES.md Added

Description of PR

This PR adds keyword arguments to validate() to use value and rtol directly instead of upper_bound and lower_bound, in response to the discussion in IAMconsortium/common-definitions#104. However, now that I've implemented this, I'm wondering whether it wouldn't make more sense to keep the pyam method lean and do the translation from value and rtol as part of a nomenclature.DataValidator class...

Any thoughts @phackstock?

[codecov]

Codecov Report

Attention: Patch coverage is 92.59259% with 2 lines in your changes missing coverage. Please review.

Project coverage is 94.9%. Comparing base (ddbb88e) to head (5789802).
Report is 31 commits behind head on main.

Files	Patch %	Lines
pyam/validation.py	91.6%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #866     +/-   ##
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- Coverage   95.0%   94.9%   -0.1%     
=======================================
  Files         64      63      -1     
  Lines       6134    6164     +30     
=======================================
+ Hits        5828    5855     +27     
- Misses       306     309      +3     

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[danielhuppmann]

After some thoughts, I concluded that implementing this feature in nomenclature makes more sense.
Closing in favor of IAMconsortium/nomenclature#370.