chore: field tags constants

[ubogdan]

Describe the PR
reduce the number of hardcoded tags.

Relation issue
None

Additional context
None

[codecov]

Codecov Report

Merging #1088 (f3b77ab) into master (557e1c6) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1088   +/-   ##
=======================================
  Coverage   94.47%   94.47%           
=======================================
  Files           9        9           
  Lines        2316     2316           
=======================================
  Hits         2188     2188           
  Misses         67       67           
  Partials       61       61           

Impacted Files	Coverage Δ
operation.go	95.86% <ø> (ø)
field_parser.go	100.00% <100.00%> (ø)

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