feat: include "self" parameter in REST handler helper functions

[kkedziak-splunk]

Issue number: ADDON-80774

PR Type

What kind of change does this PR introduce?

• Feature
• Bug Fix
• Refactoring (no functional or API changes)
• Documentation Update
• Maintenance (dependency updates, CI, etc.)

Summary

Changes

This PR introduces an additional and alternative way of specifying helper methods.

Previously:

def validate_input(definition: smi.ValidationDefinition):
    ...


def stream_events(inputs: smi.InputDefinition, event_writer: smi.EventWriter):
    ...

Now, there is also another way (with self):

def validate_input(self, definition: smi.ValidationDefinition):
    ...


def stream_events(self, inputs: smi.InputDefinition, event_writer: smi.EventWriter):
    ...

User experience

Currently used helper modules will work as before.

Checklist

If an item doesn't apply to your changes, leave it unchecked.

Review

• self-review - I have performed a self-review of this change according to the development guidelines
• Changes are documented. The documentation is understandable, examples work (more info)
• PR title and description follows the contributing principles
• meeting - I have scheduled a meeting or recorded a demo to explain these changes (if there is a video, put a link below and in the ticket)

Tests

See the testing doc.

• Unit - tests have been added/modified to cover the changes
• Smoke - tests have been added/modified to cover the changes
• UI - tests have been added/modified to cover the changes
• coverage - I have checked the code coverage of my changes (see more)

Demo/meeting:

Reviewers are encouraged to request meetings or demos if any part of the change is unclear

[github-actions]

Code Coverage 🎉

Type	PR	Develop	Change	Status
Line Coverage	88.26%	88.21%	0.05%	🟢 Increased
Branch Coverage	81.93%	81.79%	0.14%	🟢 Increased

[soleksy-splunk]

lgtm, just one question

[soleksy-splunk]

Do you need this inspect here?

[hetangmodi-crest]

We would have to make changes to input.module-template file also.

[hetangmodi-crest]

The drawback with this implementation is - when the add-on has this code and is deployed in Splunk environment and when the modinput is invoked, it will check whether the input_helper module has 2 parameters or 3, and then execute it.
I think, we could do this same during the ucc-gen build process itself and write this file accordingly. Perhaps, something like this. The drawback here is the *pyc that would be generated, which we would have to clean-up.
What do you think?