[Feature] Update spine logic for `salesforce_history` models

[fivetran-catfritz]

Is there an existing feature request for this?

• [X] I have searched the existing issues

Describe the Feature

In this PR, we updated the logic of the model int_salesforce__date_spine, which is used in salesforce__daily_activity. The salesforce__*_history models should also be updated to use similar coalesce logic, as well as the dbt_utils.get_single_value macro. This will help keep the logic consistent and simplify the code a bit.

The models affected are:

• salesforce__account_daily_history
• salesforce__contact_daily_history
• salesforce__opportunity_daily_history

Describe alternatives you've considered

No response

Are you interested in contributing this feature?

• [ ] Yes.
• [ ] Yes, but I will need assistance and will schedule time during your office hours for guidance.
• [ ] No.

Anything else?

No response