Add ability to change space key

Problem Definition

Sometimes the target Confluence application might already have existing data and consequently an existing space with the same space key that we would like to migrate/import, in which case the space import would fail saying the space key already exists.

Suggested Solution

Add the ability to change the space key during the plan configuration.

Why this is important

Scenario 1:
The known workaround is to manually edit the XML files and search/replace the old space key with a new space key, which is an error prone task and might lead to subsequent parsing errors if the XML is not edited properly. And this manual step needs to be done "the old way" outside the scope of the Migration Assistant plugin by manually exporting the space to XML, changing the files and manually importing the space.

Scenario 2:
Confluence Server can contain any invalid (i.e., non-alphanumeric) space-key. In that case, CCMA better have a validation function and offer the ability to change space-key.

Workaround

https://confluence.atlassian.com/confkb/how-to-copy-or-rename-a-space-in-confluence-169578.html