feat: improve typings for lighthouse and shared

[ahnpnl]

Summary

When trying to use this package in a Cypress project with TypeScript, I ran into several errors with typings. For example:

// TypeScript said the functions `prepareAudit` and `lighthouse`  are not defined
import { prepareAudit, lighthouse } from '@cypress-audit/lighthouse';

export const lighthousePlugin: Cypress.PluginConfig = (on, config) => {
    on('before:browser:launch', (_browser, launchOptions) => {
        prepareAudit(launchOptions);
    });

    on('task', {
        lighthouse: lighthouse(),
    });

    return config;
};

• Add cypress to root package.json. This will allow IDE to recognize /// <reference types="cypress" />
• Update index.d.ts in packages/lighthouse
• Add index.d.ts in packages/shared
• Add types to package.json for both packages/lighthouse and packages/shared
• Add .eslintignore to ignore .d.ts

cc @mfrachet

[mfrachet]

Thanks for the contribution 🙏🏻