Add deploy_token_type column to the deploy_tokens table

What does this MR do?

The first step to introduce group deploy tokens is to add a new column in the deploy_tokens table. Mirroring the architecture applied onto the Clusters::Cluster model, the aim of this new column is to tell whether a deploy token is at the project level or at the group level.

This MR includes a migration that uses a add_column_with_default statement (docs: https://docs.gitlab.com/ee/development/migration_style_guide.html#adding-columns-with-default-values)

Once this MR is merged, the development of the actual update of deploy token framework will be dealt with in this MR !23460 (merged)

Screenshots

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

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

Related to #21765 (closed)