Make tag name configurable

[blink1073]

Make the tag name used for the release configurable.
Also fix a log message that was using the wrong step name.

[blink1073]

cc @Carreau

[codecov-commenter]

Codecov Report

Merging #145 (f708f4d) into master (5af9ea7) will decrease coverage by 0.06%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##           master     #145      +/-   ##
==========================================
- Coverage   85.50%   85.43%   -0.07%     
==========================================
  Files          17       17              
  Lines        2104     2108       +4     
  Branches      253      254       +1     
==========================================
+ Hits         1799     1801       +2     
- Misses        213      215       +2     
  Partials       92       92              

Impacted Files	Coverage Δ
jupyter_releaser/tests/test_cli.py	99.16% <ø> (ø)
jupyter_releaser/cli.py	90.69% <75.00%> (+0.03%)	⬆️
jupyter_releaser/lib.py	83.79% <100.00%> (+0.13%)	⬆️
jupyter_releaser/npm.py	79.71% <0.00%> (-1.45%)	⬇️
jupyter_releaser/util.py	69.27% <0.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 5af9ea7...f708f4d. Read the comment docs.