feat: Update examples to use hubspot.serverless for calling app functions

[tamara-at-hubspot]

This change was previously introduced in #49 then reverted in #59, because we did not have product rollout lined up. I'm submitting this change again to finish the swing. We are hoping to have the examples updated and the API officially documented by the end of the month.

Description

• We are introducing a simpler API, hubspot.serverless, for calling app functions in @hubspot/ui-extensions@0.8.5.
• Note that the runServerlessFunction way still works.
• See an example migrating from runServerlessFunction to hubspot.serverless.

This PR is best reviewed by commits.

Usage

With promise syntax:

import { hubspot } from "@hubspot/ui-extensions";

hubspot.extend(() => <Extension />);

const Extension = () => {
  const handleSubmit = () => {
    hubspot
      .serverless("func-name", {
        // options, if any (e.g., propertiesToSend or parameters)
      })
      .then((response) => {
        // handle response, which is the value returned from the function on success
      })
      .catch((error) => {
        // handle error, which is an Error object if the function failed to execute
      });
  };
  return <Button onClick={handleSubmit} label="Click me" />;
}

With async/await syntax:

import { hubspot } from "@hubspot/ui-extensions";

hubspot.extend(() => <Extension />);

const Extension = () => {
  const handleSubmit = async () => {
    try {
      const response = await hubspot.serverless("func-name", {
        // options, if any (e.g., propertiesToSend or parameters)
      });
      // handle response, which is the value returned from the function on success
    } catch (error) {
      // handle error, which is an Error object if the function failed to execute
    };
  };
  return <Button onClick={handleSubmit} label="Click me" />;
}

[atanasiuk-hubspot]

LGTM