Update db/structure.sql with missing check constraint

What does this MR do?

With db/migrate/20201021085007_create_analytics_devops_adoption_segments.rb in !45748 (merged) we created a new table analytics_devops_adoption_segments with max length constraint on column name but we missed it in db/structure.sql .

This MR is fixing this.

See !45748 (comment 440333331).

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Does this MR meet the acceptance criteria?

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