Add Conda (formerly: RoboStack) installer

[Tobias-Fischer]

Hi there,

This PR adds an installer for https://github.com/RoboStack/ros-noetic. This patch is already included in the conda-forge build of rosdep (see https://github.com/conda-forge/rosdep-feedstock). It works as intended on Linux, macOS and Windows, and has for example been used to install dependencies using rosdep in our proposed cross-platform CI for moveit (see moveit/moveit#2604).

It requires ros-infrastructure/rospkg#224 to be merged first.

/cc @wolfv @traversaro @nuclearsandwich

[tfoote]

As mentioned at ros-infrastructure/rospkg#224 (comment) we'll switch this to be called Conda and the Robostack will be a required element.

[codecov-commenter]

Codecov Report

Merging #810 (3a01aec) into master (30a25a7) will decrease coverage by 0.89%.
The diff coverage is 31.88%.

@@            Coverage Diff             @@
##           master     #810      +/-   ##
==========================================
- Coverage   74.96%   74.07%   -0.90%     
==========================================
  Files          42       43       +1     
  Lines        3283     3390     +107     
==========================================
+ Hits         2461     2511      +50     
- Misses        822      879      +57     

Impacted Files	Coverage Δ
src/rosdep2/platforms/conda.py	26.56% <26.56%> (ø)
src/rosdep2/__init__.py	79.31% <100.00%> (+0.36%)	⬆️
src/rosdep2/gbpdistro_support.py	95.53% <100.00%> (+0.12%)	⬆️
src/rosdep2/sources_list.py	85.58% <0.00%> (-1.00%)	⬇️
src/rosdep2/shell_utils.py	100.00% <0.00%> (ø)
src/rosdep2/main.py	48.86% <0.00%> (+0.03%)	⬆️
src/rosdep2/platforms/source.py	90.60% <0.00%> (+0.05%)	⬆️
src/rosdep2/rospkg_loader.py	94.44% <0.00%> (+0.24%)	⬆️
src/rosdep2/lookup.py	88.17% <0.00%> (+0.34%)	⬆️
src/rosdep2/platforms/pip.py	64.00% <0.00%> (+0.48%)	⬆️
... and 3 more

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[Tobias-Fischer]

Hi @nuclearsandwich - just letting you know that the tests are passing now, after having merged ros-infrastructure/rospkg#224. So this PR is ready for review now :)