Add CCSID parameter to the connector configuration

[theodore-evans]

Description

Fixes #124

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

No additional tests added for this feature

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[theodore-evans]

I have put this PR back into draft status, as this connector as it stands does not populating missing configuration values with defaults in the standard way--i.e. defining a subclass of AbstractConfiguration (see step 1 of https://www.confluent.io/blog/create-dynamic-kafka-connect-source-connectors/)

This means that changes as they are will cause the connector to fail where no mq.ccsid config value is set. A fix with default handling for this field is upcoming.

[Joel-hanson]

Given the last comment we feel there is a better way of doing this.