Add LazyInit class to only init when getting attribute of pymongo.MongoClient

[dachengx]

Close #58

The LazyInit will only initialize the instance only if the attribute or method of pymongo.MongoClient like find.

[cfuselli]

Hey,

I think these changes make sense in general, but unfortunately I lack some knowledge on admix to understand when and where these functions are used, so please do not take my comments too seriously.

But, here are some questions:

• why is it needed to initialise the functions in the utils.py at all? Why not just call the utilix function directly in the donwloader.py? it seems like a not needed duplication to me..
• just wanted to stress that those are 1t functions, took me a while to notice that ;)

[dachengx]

re these functions are used, so please do not take my comments too seriously.

I guess initially these instances are initialized in utils.py so that we do not need to make the connection in each function.

How to optimize this depends on how often these functions are called. I do not have enough knowledge either. This PR is just an expedient that can lower the DB connection.

[lucascottolavina]

I had a look only now the code and it seems it does well its job. I validate it now, but before merring I suggest for a sake of safety, to also try it on a real scenario with a stress test to verify that it does what it promises to do