EINV-4248 : eInvoicing API definition to the Xero-OpenAPI spec

[samyuktha-sajja-xero]

Description

• Added eInvoicing API definition.
• https://xero.atlassian.net/browse/EINV-4248

Release Notes

Screenshots (if appropriate):

Types of Changes

• [ ] Bug fix (non-breaking change that fixes an issue)
• [x] New feature (non-breaking change that adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

[github-actions[bot]]

PETOSS-387

[github-actions[bot]]

Thanks for raising an issue, a ticket has been created to track your request

[0GH4J]

this one is to remain in draft because it is in a closed beta