feat: Support for postgis database

[EverWinter23]

This adds support for PostGis database which is
also supported officially by django-- geodjango.

Refrences: #41 #90 #140

[EverWinter23]

@asherf Why does the test_cache.py fail? Could you help me with it. I'm really keen to resolve this one, and by the looks of it, it is a commonly requested feature.

Can't connect to redis-- but why? Any insight would be appreciated.

[asherf]

I'll take a look at the redis failure later this week.

[asherf]

@EverWinter23 can you try rebasing and re-pushing ?
I think I merged a fix for the redis issue you are seeing in travis.

[asherf]

@EverWinter23 I also merged #218
which means you will have to update your tests to take the new labels into account.
currently running this tests for PR produces an error:

______________________ TestPostgisDbMetrics.testCounters _______________________
self = <testapp.test_db.TestPostgisDbMetrics testMethod=testCounters>
    def testCounters(self):
        r = self.saveRegistry()
        cursor = connections["postgis"].cursor()
    
        for _ in range(20):
            cursor.execute("SELECT 1")
    
        self.assertMetricCompare(
            r,
            lambda a, b: a + 20 <= b < a + 25,
            "django_db_execute_total",
            alias="postgis",
>           vendor="postgis",
        )
testapp/test_db.py:185: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
../../testutils.py:163: in assertMetricCompare
    % (metric_name, self.formatLabels(labels), saved_value, current_value),
E   AssertionError: True is not false : 
E   django_db_execute_total{alias="postgis",vendor="postgis"} was None after.
E   Value before: None
E   Value after: None

[EverWinter23]

@asherf Thanks! I'll take a look.

[EverWinter23]

@asherf Yay!!! Almost there failing for python3.8.

Update: Linting error 🤦

[EverWinter23]

@asherf Fails for python3.8-- says Imports incorrectly ordered, I've run the particular file with isort on python3.7.4, no warnings/errors. Do I need to check for python3.8 specifically? Other than that looks good to go.

[EverWinter23]

Finally!!!

[EverWinter23]

@asherf Ready for review.

[asherf]

this is not needed.
See https://help.semmle.com/wiki/display/PYTHON/Unnecessary+pass

[EverWinter23]

Got it. Why is it there in mysql/base.py and postgresql/base.py?

[EverWinter23]

Removed this block.

[asherf]

lgtm, minus the nitpick comment.
(which we should actually check with a linter..., I'll be adding that)

[asherf]

thanks for adding this feature!

[EverWinter23]

No problem. Needed it badly.