Change the documentation to refer to the new CLI tool (ibexa_cloud) instead of platform.

Message from platform.sh:

We have released the CLI included in Ibexa vendor-box, which means that Ibexa Cloud now have its own personalized CLI 
As you know, we made a few changes on our APIs this summer, and since then, users had to create an ibexa_cloud alias to use the CLI with their Ibexa Cloud projects (as indicated in your docs here), which was necessary to ensure that requests are going through the correct API proxy.
This is not required anymore, and users should now install the CLI from the vendor-box, using the following URL => https://cli.ibexa.co/
This change should therefore be communicated to users, and the documentation updated, so that they can delete the alias and use the new CLI instead (also because it seems that some users have recently had problems with the alias).
The CLI command name will remain the same (ibexa_cloud) once installed.

Anything about the alias that has been used as a workaround in the meantime must be removed.