fix: nuxt env naming convention for directus url

[Sandros94]

Types of changes

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

Description

Didn't open an Issue for this, but basically since the changes in #127 the default value for directus.url hasn't been updated to follow the naming convention of the public runtimeConfig env variables

Quoting the docs:

Anything under public and app will be exposed to the frontend as well. Values are automatically replaced by matching env variables at runtime, e.g. setting an environment variable NUXT_API_KEY=my-api-key NUXT_PUBLIC_BASE_URL=/foo/ would overwrite the two values in the example below.
Example:

 export default {
   runtimeConfig: {
     apiKey: '' // Default to an empty string, automatically set at runtime using process.env.NUXT_API_KEY
     public: {
       baseURL: '' // Exposed to the frontend as well.
     }
   }
 }

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes (if not applicable, please state why)

[Sandros94]

P.S: idk why github forced me to include the merge commits. Any ideas on how could I drop them from this PR?

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