Default currency per tenant

**Is your feature request related to a problem? Please describe.**
I'm a user of a multi-tenanted Metabase and want to create my own questions. When I use a currency column and do some stuff... bam, I get the default currency of the instance as a suggestion but I want to have my own currency as a default (can/can not be the same as the locale)

**Describe the solution you'd like**
default currency could be another choice like the language

**Describe alternatives you've considered**
None

**How important is this feature to you?**
Requested by a customer

**Additional context**
NA

The issue does not name files, tests, or entry points. Start by locating how the instance default currency is configured and how tenant-specific settings are represented; done means a tenant can choose a default currency independently of the instance currency and have it suggested for currency columns.

Written by the indexing model from the issue text.