feat: add-api-proxy: Add Nitro server API routes

[vloss3]

Solves #165

[TurtlBbx]

@vloss3 Once the improvements are done, could you add a test case for when the exposeAPIRouteRules option is set to false. It can be a copy of https://github.com/drunomics/nuxtjs-drupal-ce/blob/2.x/test/basic.test.ts with the exposeAPIRouteRules set to false.

[TurtlBbx]

@vloss3 README needs to be updated as well for this feature.

[vloss3]

The following was discussed to move forward with this feature:

New options:

• drupalBaseUrl: origin URL, for iframes and other cases, changeable via env variable
• serverDrupalBaseUrl: http://node (optional: use this during server render if set))
• ceApiEndpoint: /ce-api (default)
• menuEndpoint: unchanged
• menuBaseUrl: http://domain.com/ce-api (default: drupalUrl + ceApiEndpoint), changeable via env variable

Note: Those options will have defaults and will not require configuration changes

Route rules changes:

• remove /api/drupal
• convert route rules to nitro server routes

Use cases to consider:

• proxy files through frontend
• add an iframe of drupal in the frontend project code

Tests and customizing cache rules(by project) will be carried in follow-up issues.

[fago]

@vloss3 I updated README slightly. I was not sure about DRUPAL_BASE_URL - do we still support that variable actually? Since there is built-in support in nuxt to override config via NUXTPUBLIC... I could see us dropping that + documenting that instead.