Rename the flexible resources page on Upsun fixed

[nicogommen]

Where on docs.platform.sh should be changed?

The Flexible resources page (https://docs.platform.sh/create-apps/flexible-resources.html) can be confusing, now that we have fixed and flexible types of org and projects, especially knowing that this setting is relevant for fixed projects only.

The suggestion is to rename this page to Advanced resource adjustment (but open to feedback for a better name).

What exactly should be updated?

The title of this page => https://docs.platform.sh/create-apps/flexible-resources.html

Additional context

No response

[gilzow]

Title of page has changed, but we need to potentially change the URL.

[gilzow]

see also #4970