Improve performance of endpoint to list pages on the Portal API

[exalate-issue-sync]

Describe the bug :

The Portal API exposes an endpoint to list all the pages of an API or retrieve a single page, for instance: /portal/environments/DEFAULT/apis/<span class="error"><span class="error">[id]</span></span>/pages

/management/organizations/DEFAULT/environments/DEFAULT/apis/[id]/pages

which takes around 200 ms to return versus

/portal/environments/DEFAULT/apis/[id]/pages

which takes around 11 seconds to return.

Same is for loading single pages:

/management/organizations/DEFAULT/environments/DEFAULT/apis/[id]/pages/[page_id]

returns in 400 ms while the portal api endpoints:

/portal/environments/DEFAULT/apis/[id]/pages/[page_id]

requires 11 seconds again

linked to #9042

Desktop :

• Environment: [e.g. 3.20.x] 3.18.14
• Browser [e.g. chrome, safari]

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