Parse relation expressions at service creation time

[vonagam]

Parse relation expressions options (allowedEager, allowedInsert and allowedUpsert) in constructor instead of passing strings for parsing every service call.

Also in types indicate that those options can be not only strings but objects too (an objection notation of a relation or a result of RelationExpression.create).

[vonagam]

Added mergeAllowUpsert and mergeAllowInsert params, work the same as mergeAllowEager for allowedEager and have the same use cases: when you want to limit relations on which a user can operate based on some criteria.

[dekelev]

Thanks, looks good!

[dekelev]

Released in v4.5.0