Add non-strict option to add_files_from_table procedure

[ebyhr]

The procedure throws an exception if column definition between a source and a target table doesn't exctly match. We could add a function argument which tweaks the validation because the schema can be a little different.

Probably, we should still disallow the following situation even if the option is enabled:

• schema is completely different: (a int) ↔︎ (y string)
• different column types with same column name: (a int) ↔︎ (a string)
  • this is allowed in Spark's add_files procedure, but it throws an exception when reading tables

Relates to #22751 (comment) by @cwsteinbach