feat: optional ciso8601

[rolincova]

Closes #98

ciso8601 is an optional dependency and has to be installed separably

• CHANGELOG.md updated
• Rebased/mergeable
• Tests pass
• Sign CLA (if not already signed)

[codecov-commenter]

Codecov Report

Merging #120 into master will decrease coverage by 0.02%.
The diff coverage is 88.23%.

@@            Coverage Diff             @@
##           master     #120      +/-   ##
==========================================
- Coverage   88.71%   88.68%   -0.03%     
==========================================
  Files          22       23       +1     
  Lines        1808     1821      +13     
==========================================
+ Hits         1604     1615      +11     
- Misses        204      206       +2     

Impacted Files	Coverage Δ
setup.py	0.00% <0.00%> (ø)
influxdb_client/client/date_utils.py	100.00% <100.00%> (ø)
influxdb_client/client/flux_csv_parser.py	91.71% <100.00%> (ø)
influxdb_client/client/write/point.py	98.30% <100.00%> (+0.01%)	⬆️

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[bednar]

LGTM