[PROPOSAL] Custom connection pooling option for connection_class=RequestsHttpConnection.

[Neckbuster]

What/Why

• Custom Connection pooling option for connection_class=RequestsHttpConnection.
• This feature is required because clients who are using advanced auth plugins options like AWS_IAM are forced to used RequestHttpConnection and are stuck with default values i.e 10 pool max_size provided in request library.

What are you proposing?

A new connection_class that will be a child class of RequestsHttpConnection with custom connection_pool option like pool_max_size that will be provided from client. The session attribute in RequestHttpConnection will be mounted with requests adapters with these pooling options.

[harshavamsi]

@Neckbuster I think this is a good idea. I see that the default connection class has the maxsize attribute. Would be nice to replicate that in the RequestHttpConnection class. Out of curiosity could you lay out your implementation idea here? To me it looks like you would not only need to update the pooling options in the session but also make use of self.pool.urlopen to allow for the actual pooling to take place?

Also can you take a stab at it with a PR?

[harshavamsi]

Closing via #216