add list path item with empty actions

[charan678]

Fixes

• api definitions has files which contain list uri and instance uri properties, but in some of the cases there are no actions defined for list uri. But this list uri are referred by different api definitions as parent url, this scenario was missed while creating empty path Item object for parent urls in OAI spec and hence this created incorrect directory structure for some domains in twilio-java.
• Adding endpoint and twiml format type to schema types

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 read the Contribution Guidelines and my PR follows them
• I have titled the PR appropriately
• I have updated my branch with the main branch
• 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

If you have questions, please file a support ticket, or create a GitHub Issue in this repository.

[childish-sambino]

nit: These aren't needed for empty paths.

[charan678]

will remove these