Batch group lookups for inherited CI variables

What does this MR do and why?

Removes the per-row queries from getInheritedCiVariables, the query behind the inherited variables list on a project's CI/CD settings page.

• groupName and groupCiCdSettingsPath loaded the variable's group and its route for every variable.
• groupCiCdSettingsPath also checked admin_cicd_variables on each ancestor group separately, and each check read the organization, namespace settings, SAML provider and member access level.

Each group is now loaded once per request with its route, and Preloaders::GroupPolicyPreloader preloads the policy data for that batch.

Measured with the frontend query:

	Before (all / uncached)	After
2 groups, 2 variables	24 / 18	19
5 groups, 25 variables	85 / 30	19

Who sees groupCiCdSettingsPath does not change. The value is the same before and after for an owner of the root group only, a project maintainer, and a maintainer of the project's group.

References

Closes #629334 (closed)

How to validate

bundle exec rspec spec/requests/api/graphql/ci/inherited_ci_variables_spec.rb spec/graphql/types/ci/inherited_ci_variable_type_spec.rb

The new request example fails without the change to inherited_ci_variable_type.rb (25 → 54 queries).