[Spark] Flip isDeltaTable.throwOnError to true (#3422)

## Description
- Change the default value of the isDeltaTable.throwOnError flag to
`true`.

## How was this patch tested?
Existing tests (was already `true` in testing).

## Does this PR introduce _any_ user-facing changes?
Resolving a Delta that is accessed by path (e.g. DeltaTable.forPath() or
SELECT ... FROM delta.<path>) will now forward exceptions thrown while
accessing , instead of always throwing a DELTA_MISSING_DELTA_TABLE
exception.
This helps locating issues such as missing access permissions without
having to through support.

spark/src/main/scala/org/apache/spark/sql/delta/sources/DeltaSQLConf.scala

@@ -1000,7 +1000,7 @@ trait DeltaSQLConfBase {
         | Delta table.
         |""".stripMargin)
       .booleanConf
-      .createWithDefault(Utils.isTesting)
+      .createWithDefault(true)
 
   val DELTA_LEGACY_STORE_WRITER_OPTIONS_AS_PROPS =
     buildConf("legacy.storeOptionsAsProperties")