archive db has blocks with no parent_id

[deepthiskumar]

1. Seeing entries in the blocks table with null values in the parent_id column. The archive node failed to add the parents of such blocks because of another issue (see the next point). I think we should make parent_id a NOT NULL field. For genesis block make parent_id point to the genesis blocks id (self-pointer)
2. Seeing the following error when adding some blocks:

    error: "Request to <postgres://postgres:_@hard-fork-archive-node-postgresql:5432/archive> failed: ERROR: duplicate key
   value violates unique constraint \"blocks_internal_commands_pkey\"\nDETAIL: Key (block_id, internal_command_id)=(119,
   59) already exists.\n Query: \"INSERT INTO blocks_internal_commands (block_id, internal_command_id, sequence_no, 
   secondary_sequence_no) VALUES ($1, $2, $3, $4)\"."
   
   

internal_command_ids could be duplicated within a block.
For example: Two different fee transfers with the same fee and same receiver; one in a fee-transfer transaction and the other in a coinbase transaction as it was in this case or two different fee transfers with the same fee and same receiver but in different fee-transfer transactions (possible when a block occupies slots in two trees of a scan state)