feat: add contribs/gnomigrate

[zivkovicmilos]

Description

This PR introduces a small tool called gnomigrate, which will serve as a helper for migrating Gno data.
Currently, it only supports transaction sheet migration from std.Tx to gnoland.TxWithMetadata.

Contributors' checklist...

• Added new tests, or not needed, or not feasible
• Provided an example (e.g. screenshot) to aid review or the PR is self-explanatory
• Updated the official documentation or not needed
• No breaking changes were made, or a BREAKING CHANGE: xxx message was included in the description
• Added references to related issues and PRs
• Provided any useful hints for running manual tests

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 63.33%. Comparing base (c776e32) to head (ef61841).
Report is 5 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3063   +/-   ##
=======================================
  Coverage   63.33%   63.33%           
=======================================
  Files         548      548           
  Lines       78600    78600           
=======================================
+ Hits        49778    49785    +7     
+ Misses      25465    25460    -5     
+ Partials     3357     3355    -2     

Flag	Coverage Δ
contribs/gnodev	61.11% <ø> (+0.62%)	⬆️
contribs/gnofaucet	14.82% <ø> (ø)
gno.land	67.35% <ø> (ø)
gnovm	67.88% <ø> (ø)
misc/genstd	79.72% <ø> (ø)
tm2	62.32% <ø> (-0.11%)	⬇️

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