Implements metadata query for complex query feature

A subfield in the resource_metadata field of the Sample
can be used in filter expression as
  metadata.<subfield_name>

Validation of the names of the metadata is not implemented

Implements: blueprint complex-filter-expressions-in-api-queries
Change-Id: Icf198f740191b5fff0008e9aa7b054c1cc33d75d
Implements "not" operator for complex query

Change-Id: Idf17b35c5f4267b9254a64e37b0d8b1b0dcbca89
Implements: blueprint complex-filter-expressions-in-api-queries
Merge "Implements metadata query for complex query feature"
Merge "Implements "not" operator for complex query"