Added custom tag

[suratdas]

During image upload it is now possible to add custom tag also. Custom tag is an optional field and it will work both with or without it.

[codecov-commenter]

Codecov Report

Merging #64 (391abe5) into master (28f6806) will not change coverage.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##              master       #64   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
  Complexity        31        31           
===========================================
  Files              5         5           
  Lines            108       109    +1     
  Branches           4         4           
===========================================
+ Hits             108       109    +1     

Impacted Files	Coverage Δ	Complexity Δ
...sion_tracker/sdk_java/VisualRegressionTracker.java	100.00% <100.00%> (ø)	22.00 <0.00> (ø)

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[pashidlos]

LGTM