[Feature] Add `time_zone` configuration for source freshness checks

### Is this a new bug in dbt-core?

- [X] I believe this is a new bug in dbt-core
- [X] I have searched the existing issues, and I could not find an existing issue for this bug

### Current Behavior

Currently, when running dbt source freshness tests in a timezone other than UTC, a query like the following is compiled:

```
select
max(convert_timezone('UTC', created_at_local)) as max_loaded_at,
convert_timezone('UTC', current_timestamp()) as snapshotted_at
from raw.jaffle_shop.orders
```

In this case, the execution order to obtain max_loaded_at is as follows:
• Convert the timezone.
• Retrieve the maximum value of created_at_local in the converted timezone.

At this stage, the timezone conversion is performed for all records, and the maximum date is then calculated from the converted timestamps. As a result, the table is fully scanned once, and aggregation is performed.

As a result, when the number of records is large, the data freshness test takes a significant amount of time.

### Expected Behavior

The ideal steps would be as follows:
• First, retrieve the latest date from the table.
• Then, perform the timezone conversion.

```
select
convert_timezone('UTC', max(created_at_local)) as max_loaded_at,
convert_timezone('UTC', current_timestamp()) as snapshotted_at
from raw.jaffle_shop.orders
```

### Steps To Reproduce

1. In a dbt-snowflake environment in
2. Create sample dbt project and set up dbt profile
3. Make sample table in snowflake for testing freshness
```
create or replace table D_HARATO_DB.SAMPLE_SCHEMA.SAMPLE_TABLE as
select '2024-11-24' as TEST_DATE ,'test' as SAMPLE_VALUES
union
select '2024-11-25' as TEST_DATE ,'test' as SAMPLE_VALUES
;
```
4. “Set up data freshness tests in dbt”
```
# _source.yml
version: 2

sources:
- name: sample_source
database: D_HARATO_DB
schema: SAMPLE_SCHEMA
description: This source includes raw order data
tables:
- name: SAMPLE_TABLE
description: Raw data for orders
freshness:
warn_after: {count: 18, period: hour}
error_after: {count: 24, period: hour}
loaded_at_field: convert_timezone('UTC', TEST_DATE)
```
5. Run `dbt source freshness`

### Relevant log output

_No response_

### Environment

```markdown
- OS:mac
- Python:3.11.6
- dbt: 1.9.0
```

### Which database adapter are you using with dbt?

snowflake

### Additional Context

This is the profile after running the freshness test. It scans the two records created and applies timezone conversion and retrieves the latest date from the scan results.