Create config.yaml for PtX module

[francescolovat]

So far, this PR adds a draft of configuration file for the PtX module in iiasa/message_data#169.

This is done for using Context methods and other utils such as load_package_data() from message_ix_models.

Depending on time availability:

• Migrate full code (excl. data sources) from message_data. Postponed for after publication.
• Documentation (migrate draft from iiasa/message_data#169)

[codecov]

Codecov Report

Merging #10 (9fef271) into main (24c8c58) will increase coverage by 31.87%.
The diff coverage is n/a.

❗ Current head 9fef271 differs from pull request most recent head dfd4d99. Consider uploading reports for the commit dfd4d99 to get more accurate results

@@             Coverage Diff              @@
##             main       #10       +/-   ##
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+ Coverage   68.12%   100.00%   +31.87%     
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  Files          75        17       -58     
  Lines        5066       647     -4419     
============================================
- Hits         3451       647     -2804     
+ Misses       1615         0     -1615     

see 75 files with indirect coverage changes