feat: add User-Agent request header, use Makefile Targets as a base for commands

[bednar]

Closes #7
Closes #4

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

[codecov-io]

Codecov Report

Merging #9 into master will increase coverage by 13.86%.
The diff coverage is n/a.

@@              Coverage Diff              @@
##             master       #9       +/-   ##
=============================================
+ Coverage     58.01%   71.88%   +13.86%     
+ Complexity      283      184       -99     
=============================================
  Files            11        8        -3     
  Lines           605      409      -196     
=============================================
- Hits            351      294       -57     
+ Misses          254      115      -139

Impacted Files	Coverage Δ	Complexity Δ
src/InfluxDB2/Client.php	100% <ø> (ø)	5 <0> (ø)	⬇️
src/InfluxDB2/DefaultApi.php	81.81% <ø> (+0.56%)	10 <0> (ø)	⬇️
src/InfluxDB2/Model/Query.php
src/InfluxDB2/Model/WritePrecision.php
src/InfluxDB2/Model/Dialect.php

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