classify neon transient error

[jgao54]

Classify a transient Neon error:

Postgres WAL error: received error response, message: &{Severity:ERROR SeverityUnlocalized:ERROR Code:XX000 Message:[walsender] Failed to read WAL (req_lsn=0/DD7D4000, len=8192): closing remote connection: requested WAL up to 0/DD7D6000, but current donor safekeeper-6.cell-4.eu-central-1.aws.neon.tech:6401 has only up to 0/DD7D5FF8 Detail: Hint: Position:0 InternalPosition:0 InternalQuery: Where: SchemaName: TableName: ColumnName: DataTypeName: ConstraintName: File:walsender_hooks.c Line:144 Routine:NeonWALPageRead UnknownFields:map[]}

Fixes: DBI-907