Integrate Elastic Search into the existing GitlabProjectAPI implementation

[epsstan]

Feature Request

Integrate Elastic Search into the existing GitlabProjectAPI implementation.

Description of Problem:

The current implementation of the ProjectAPI iterates through all Gitlab projects and filters the projects with the Legend tag.
This is "slow" as it makes multiple network calls to the Gitlab API.

Potential Solutions:

The Gitlab Enterprise Edition offers Elastic Search indexing. Instead of iterating over all projects we can search for Legend projects.

Note : Elastic Search Indexing is not available on the community edition. We have to support both the Enterprise and Community Editions.