feat(dev): Add Git pre-commit hooks [gapic-generator-python]

[miraleung]

After copying this into .git/hooks as described in DEVELOMPENT.md, these checks (a subset of CI tasks) will run locally on each commit.

[codecov]

Codecov Report

Merging #908 (1024c1d) into master (7c185e8) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #908   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           26        27    +1     
  Lines         1608      1697   +89     
  Branches       328       347   +19     
=========================================
+ Hits          1608      1697   +89     

Impacted Files	Coverage Δ
gapic/samplegen_utils/types.py	100.00% <ø> (ø)
gapic/samplegen_utils/utils.py	100.00% <ø> (ø)
gapic/utils/case.py	100.00% <ø> (ø)
gapic/utils/reserved_names.py	100.00% <ø> (ø)
gapic/generator/generator.py	100.00% <100.00%> (ø)
gapic/samplegen/samplegen.py	100.00% <100.00%> (ø)
gapic/schema/api.py	100.00% <100.00%> (ø)
gapic/schema/metadata.py	100.00% <100.00%> (ø)
gapic/schema/wrappers.py	100.00% <100.00%> (ø)
gapic/utils/__init__.py	100.00% <100.00%> (ø)
... and 3 more

---

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 54033ee...1024c1d. Read the comment docs.