Move `Gitlab::Ci::Pipeline::Seed::Deployment/Environment` to a service classes

Problem

Seed::Deployment and Seed::Environment were introduced for creating deployment records in the same transaction with ci_builds, however, this logic was changed due to the recent database decomposition effort for ci_* tables.

Since these Seed classes are not used in the way of typical Seed classes, we should move the business logic to service classes.

Proposal

• Create a corresponding service class (services/*.rb)
• Move the business logic to there.