Allow mapping multiple topics to single container in sink connector

[benjaminrhope]

## Problem Statement
I want to map multiple topics to one single cosmos db container like this:

"connect.cosmos.containers.topicmap": "topicA#container,topicB#container"

This is currenltly not supported since TopicContainerMap uses the BidiMap data structure, which only allows for a 1-1 relationships.

## Proposed Solution
Allow multiple topics to map to one single container by allowing many-to-one relationships in TopicContainerMap.

Next Steps

• Team consensus to proceed
• Schedule Design Session
• Complete Design Review

[ryancrawcour]

This should be easy to implement. Take the provide a config for topicMap, and parse the string on topic#container.
Need to consider what to do if -
a) that config is not provided,
b) does this make another config redundant and therefore a breaking change
c) what to do if the string is supplied in the incorrect format.