Remove OIDS from `ag_graph`

[emotionbug]

Since PG 12 does not recommend and not allow to use the use of Oids, so removed Oids. Oid uses 4Byte, it uses INT type for compatibility. and, create a sequence of "$TABLE_NAME$_$COLUMN_NAME$_seq" and calls it to create a new ID.

And, due to the rule that a value less than 1 cannot exist, the case where it does not exist is considered 0 (INVALID_AG_GRAPH_ID).

[deem0n]

Also, if you dump & restore, after that you'll get age crashes. You need to manually fix oids in the ag_graph & ag_label tables. I have a plsql procedure for that, but it will be unnecessary if we remove OIDs.

[emotionbug]

@jrgemignani rebased master.