Add User.location to GraphQL API

What does this MR do?

This adds a field to the GraphQL API which is present in the REST API. Specifically location.

GraphQL queries

query {
 currentUser {
   name
   location
 }
}

Representative result:

{
  "data": {
    "currentUser": {
      "name": "Alex Kalderimis",
      "location": "Cambridge, UK"
    }
  }
}

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

This MR exposes an additional field that is already available through the REST API. It does not present any new risks, and the nature of GraphQL is that new fields do not affect existing queries.

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

Security

This MR exposes Personally Identifying Information (PII), so requires a security review. This is currently protected by the policy :read_user (which is the same as for the users/:username REST endpoint).

We could potentially further protect this behind :read_user_location.

• 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