feat: use select_related to fetch types in CSVLoader

[Ali-D-Akbar]

PROD-4237
Adds select_related to Eager load CourseType and CourseRunType for Courses and CourseRuns respectively in CSVLoader

[AfaqShuaib09]

nit: commit type can be perf instead of feat

[DawoudSheraz]

do we have stats on how does this improve the overall filtering?

[Ali-D-Akbar]

do we have stats on how does this improve the overall filtering?

>>> # Without select_related
>>> start_time = time.time()
>>> course = Course.objects.filter_drafts(key='edX+DemoX').first()
>>> if course:
...     uuid = str(course.type.uuid)  # This triggers an additional query
... 
>>> end_time = time.time()
>>> print(f"Without select_related: {end_time - start_time:.4f} seconds")
Without select_related: 0.0395 seconds
>>> 
>>> # With select_related
>>> start_time = time.time()
>>> course = Course.objects.filter_drafts(key='edX+DemoX').select_related('type').first()
>>> if course:
...     uuid = str(course.type.uuid)  # No additional query
... 
>>> end_time = time.time()
>>> print(f"With select_related: {end_time - start_time:.4f} seconds")
With select_related: 0.0058 seconds

[DawoudSheraz]

While it does not achieve much individually but it might prove a bit helpful when running loader against large set of data.