Add package maintainer information to metadata

[cottsay]

This information could be useful to other extensions.

[codecov[bot]]

Codecov Report

Merging #484 (c7c99bf) into master (d8e455e) will increase coverage by 0.07%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #484      +/-   ##
==========================================
+ Coverage   81.01%   81.09%   +0.07%     
==========================================
  Files          59       59              
  Lines        3556     3570      +14     
  Branches      682      687       +5     
==========================================
+ Hits         2881     2895      +14     
  Misses        629      629              
  Partials       46       46              

Impacted Files	Coverage Δ
colcon_core/package_augmentation/python.py	90.24% <100.00%> (+2.00%)	:arrow_up:

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[mikepurvis]

We're working on a port of catkin-tools-document to the colcon ecosystem and this kind of thing is pretty useful for that. 👍