fix applications response types

[s-lukashenka-micoworks]

• Applications API response type is missing a privateKey field.
• Applications API does not require all the three webhook URLs to be passed during creation but the type does not allow to omit any.

Description

Motivation and Context

This PR helps resolve failing type checks. The API itself works fine and has the mentioned field in its response.
Related to #955.

Testing Details

Not sure if I did things right but I ran the test suite on the PR branch.
Please, let me know if some other tests or changes are needed.

Example Output or Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[manchuck]

Update to be:

This will only be present when the application is created, or when you cycle the public key when doing an update

[s-lukashenka-micoworks]

@manchuck updated the doc 🙇