Advanced search: Add planner role support to commits

Problem to solve

The planner role was introduced in #482733 (closed).

Commits search is dependent upon project visibility_level and repository access level. Advanced search (Elasticsearch) currently does not grant the planner role access to the commits scope, even though planner users should be able to view commits wherever they can view the repository.

Proposal

Fully implement the planner role for commit search. The Elastic::Latest::GitClassProxy class (using Elastic::Latest::CommitConfig) is where the Elasticsearch query for commits is built.

note: Need to confirm whether planner support applies to public/internal projects only or all visibility levels (see &17674 footnote 2). Also update the role and permissions documentation since it still states the Reporter role is required to view code/commits.