Rename KPAccountCreator class and add comments class and add comments

[ugoamanoh]

The class KPAccountCreator should be renamed to something more intuitive and comments to be added for a better understanding of what the class is doing

Acceptance criteria:

• KPAccountCreator to be renamed to KeyPairAccountCreator
• kdoc comment describing high level functionality of class
• kdoc comment describing AccountCreator interface
• Existing tests must pass (after rename)
• breaking change from rename marked in changelog

No new tests needed but they won't be rejected if any are added :)

_{This is mirroring #161718980 in pivotal}

[mirceanis]

is KeyPairAccountCreator more meaningful?

[ugoamanoh]

yes