[Feature] make staging `log` model an append-strategy incremental table

### Is there an existing feature request for this?

- [X] I have searched the existing issues

### Describe the Feature

Add logic to `stg_fivetran__log` to make it an incremental model. Since past records should not change at all once they are inserted, an [append](https://docs.getdbt.com/reference/resource-configs/glue-configs#the-append-strategy) strategy would work great here and hopefully limit runtime a bunch!

### Describe alternatives you've considered

- keep it non-incremental
- the `log` table can get super big and unwieldy
- use another incremental strategy:
- too complicated for what we need, though we need to be very careful to not insert duplicate records

### Are you interested in contributing this feature?

- [X] Yes.
- [ ] Yes, but I will need assistance and will schedule time during your [office hours](https://calendly.com/fivetran-solutions-team/fivetran-solutions-team-office-hours) for guidance.
- [ ] No.

### Anything else?

_No response_