fix: add batch_id as optional argument when creating invoice payment

[Russell-Pollari]

Fixes: #30

Add batch_id as optional argument when creating invoice payment.

Previously creating an invoice payment would always create a new batch

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have titled the PR appropriately
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• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation about the functionality in the appropriate .md file
• I have added inline documentation to the code I modified

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