Add composite organization_id, id index on projects table

The following discussion from !136811 (merged) should be addressed:

• @abdwdd started a discussion: (+2 comments)

  consider replacing the existing index on organization_id to be a composite index: organization_id, id. The index might not be used immediately, but once we start adding more organizations, the new index should help out a bit.

The existing index needs to be removed. Consider getting a review from @ahegyi as he suggested this improvement.