feat: add DataToPoint utility to convert a custom struct to a write Point

[sranka]

Proposed Changes

This PR adds a new write.DataToPoint function that converts custom structures to write.Point, the code uses the tags/annotations from v3 client proposal to map structure fields to line protocol parts.

See also #389

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• A test has been added if appropriate
• Tests pass
• Commit messages are in semantic format
• Sign CLA (if not already signed)

[bednar]

LGTM 🚀

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (c1da0c5) 92.72% compared to head (425a783) 92.94%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #394      +/-   ##
==========================================
+ Coverage   92.72%   92.94%   +0.21%     
==========================================
  Files          23       25       +2     
  Lines        2242     2310      +68     
==========================================
+ Hits         2079     2147      +68     
  Misses        123      123              
  Partials       40       40              

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