Add application size validations for ci_builds columns

We have a few columns in the ci_builds table with type varchar 255, but we don't have any model validations for them. We should add validations to match, but this is a breaking change for self-managed because there is no limit at the column level for new installs: #321685

• status
• stage
• ref
• type
• target_url
• description

This validation must be implemented under a feature flag called ci_builds_columns_size_validation.