Add Validations for Operations Strategy Model

What does this MR do?

Add validations for the Operations::Strategy model.

Validate that name is one of the 3 Unleash strategies we currently support.

Validate that parameters are valid for the given strategy type.

Reference: https://unleash.github.io/docs/activation_strategy

This copies the current validations for the Operations::FeatureFlagScope model, which is what our current feature flag implementation uses.

• https://gitlab.com/gitlab-org/gitlab/-/blob/12ac49bf19aaf0cb3a4294bd6613f6600fb46df6/ee/app/models/operations/feature_flag_scope.rb#L21
• https://gitlab.com/gitlab-org/gitlab/-/blob/12ac49bf19aaf0cb3a4294bd6613f6600fb46df6/ee/app/validators/feature_flag_strategies_validator.rb

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

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• 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
• Security reports checked/validated by a reviewer from the AppSec team