EZP-23742: Add PlatformUI bundles to ezpublish-community composer.json

JIRA: https://jira.ez.no/browse/EZP-23742 (sub-task of https://jira.ez.no/browse/EZP-23128 and thus requires https://github.com/ezsystems/PlatformUIBundle/pull/136)

# Description

Adds the PlatformUIBundle dependency to ezpublish-community. It also changes the default REST Auth method to session (until [maybe we can support both](https://jira.ez.no/browse/EZP-22192))

# Tests

manual tests
as written in the description, until we can support both auth method (https://jira.ez.no/browse/EZP-22192), we don't have the choice.