feat: client can be used as a resource

[bednar]

Closes #120

Proposed Changes

The InfluxDB::Client can be also used as a resource:

InfluxDB2::Client.use('https://localhost:8086', 'my-token') do |client|
  client.do_something
end

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• A test has been added if appropriate
• rake test completes successfully
• Commit messages are conventional
• Sign CLA (if not already signed)

[codecov-commenter]

Codecov Report

Base: 48.19% // Head: 48.22% // Increases project coverage by +0.02% 🎉

Coverage data is based on head (728273c) compared to base (7297785).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #127      +/-   ##
==========================================
+ Coverage   48.19%   48.22%   +0.02%     
==========================================
  Files          77       77              
  Lines        7942     7946       +4     
==========================================
+ Hits         3828     3832       +4     
  Misses       4114     4114              

Impacted Files	Coverage Δ
lib/influxdb2/client/client.rb	100.00% <100.00%> (ø)

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