Conda ci

[marscher]

• Add the conda-forge feedstock recipe here to be run regularly along the other jobs. It just performs the build and does not run the testsuite, because the tests are already run on the other configurations.
• Re-add Python 3.8 and 3.9 to CI.
• Use our own python template in Azure to download Python versions.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.10%. Comparing base (5cb418d) to head (f6b7f76).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1361      +/-   ##
==========================================
- Coverage   86.26%   86.10%   -0.16%     
==========================================
  Files         113      112       -1     
  Lines       10551    10273     -278     
  Branches     4045     4044       -1     
==========================================
- Hits         9102     8846     -256     
+ Misses        845      822      -23     
- Partials      604      605       +1     

Files with missing lines	Coverage Δ
native/python/pyjp_value.cpp	78.61% <ø> (ø)

... and 2 files with indirect coverage changes

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