sql: change information_schema routines data types

[mnovelodou]

Previously, information_schema routines at columns interval_precision,
result_cast_char_octet_length and result_cast_datetime_precision have
STRING data type
This was inadequate because at postgres these columns are expected to
be INT data type
To address this, this patch changes the data types to INT

Release note (sql change): Changed information_schema.routines data
types at columns interval_precision, result_cast_char_octet_length
and result_cast_datetime_precision to INT

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[cockroach-teamcity]

This change is 

[RichardJCai]

bors r+

[craig]

Build succeeded:

• GitHub CI (Cockroach)