Support plain timestamp type (oid 1114)

[kayhide]

Support plain timestamp type (timestamp without timezone) which is mapped to oid of 1114.

Currently it has timestampType and is mapped to oid 1184 as:

selda/selda-postgresql/src/Database/Selda/PostgreSQL/Encoding.hs

Lines 30 to 47 in 33f76cf

	-- | OIDs for all types used by Selda.
	blobType, boolType, intType, int32Type, int16Type, textType, doubleType,
	dateType, timeType, timestampType, nameType, varcharType, uuidType,
	jsonbType :: Oid
	boolType = Oid 16
	intType = Oid 20
	int32Type = Oid 23
	int16Type = Oid 21
	textType = Oid 25
	nameType = Oid 19
	doubleType = Oid 701
	dateType = Oid 1082
	timeType = Oid 1266
	timestampType = Oid 1184
	blobType = Oid 17
	varcharType = Oid 1043
	uuidType = Oid 2950
	jsonbType = Oid 3802

Plain timestamp type is necessary when reading a table which is created by some other library/framework.

[kayhide]

On our application, we make all timestamps to be saved in utc and use only oid 1114.
In such a case, just replacing the 1184 with 1114 works.

But of course, it is not a good solution as a library...