[postgresql] Import into temp table

[AlexeyShirshov]

In postgre temp table exists in special schema (pg_temp_) which is optional. You can omit it when access table, but in TableInfo.LoadData method schema is required (it is optional only for SqlServer).
You should make it optional for postgresql too.

[MIKron1991]

I had the same issue. I think we should set BulkConfig.CustomDestinationTableName to some "my_temp_table" without scheme and it would be fine, but for that we need replace :

EFCore.BulkExtensions/EFCore.BulkExtensions/TableInfo.cs

Line 197 in 54463ab

Schema = customSchema ?? entityType.GetSchema() ?? defaultSchema;

on
Schema = customTableName != null ? customSchema : entityType.GetSchema() ?? defaultSchema;

@borisdj I can contribute, if you don't mind.

[borisdj]

@MIKron1991 sure, make a PR.

[MIKron1991]

@MIKron1991 sure, make a PR.

Done.
#1449
#1450

[borisdj]

Merged, thx for contrib.