Implement basic InfluxDB client

[wcoenraads]

Closes #6. Implements a very simple InfluxDB client using their REST API. It can connect to the database, retrieve a specified timeseries, and return it as a dataframe with two columns (time and value). This client does not (yet) escape any parameters it gets, so it should not be used with untrusted input.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 12 lines in your changes are missing coverage. Please review.

Project coverage is 56.57%. Comparing base (2e1f48e) to head (52fdd32).
Report is 1 commits behind head on main.

Files	Patch %	Lines
src/influx.jl	0.00%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #16      +/-   ##
==========================================
- Coverage   61.42%   56.57%   -4.85%     
==========================================
  Files           3        4       +1     
  Lines         140      152      +12     
==========================================
  Hits           86       86              
- Misses         54       66      +12     

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