Add Version Column to Operations Feature Flags Table

What does this MR do?

Add a version column to the operations_feature_flags table.

Based on the PoC, this should be useful for validations and as a single source of truth for the version of a feature flag. version can be 1 for a legacy flag or 2 for a new flag.

In the PoC...

• Legacy flags (version 1) can have associated operations_feature_flag_scopes rows / models.
• New flags (version 2) can have associated operations_strategies rows / models.

Issue: #204895 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

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• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
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