Fix Id bigint conversation for not yet created table

[ongkong]

Tracking issue

#3966

Why are the changes needed?

This commit fixes a bug with migrations. The previous code was modifying a table (description_entities) that does not exists yet when the migration is ran in order.

What changes were proposed in this pull request?

Only modify id column of tables that exist already.

How was this patch tested?

N/A

Check all the applicable boxes

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

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[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 59.11%. Comparing base (f5f8230) to head (5e78483).

Files	Patch %	Lines
flyteadmin/pkg/repositories/config/migrations.go	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5157      +/-   ##
==========================================
+ Coverage   59.10%   59.11%   +0.01%     
==========================================
  Files         645      645              
  Lines       55574    55574              
==========================================
+ Hits        32846    32852       +6     
+ Misses      20135    20129       -6     
  Partials     2593     2593              

Flag	Coverage Δ
unittests	59.11% <33.33%> (+0.01%)	⬆️

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[eapolinario]

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