Allow to set non-Discover default page for app management

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

Opening "Apps" now lands on a new "Discover" page added in v29:
https://[domain]/settings/apps/discover.

It means that in almost all cases, one needs to manually select an actual apps
page to see available updates, installed apps or do upgrades.

If there is an option to hide this panel, I couldn't find it.

Steps to reproduce

1. Click 'Apps' on the use menu in the upper right corner.
2. "Discover" advertising page appears.

Expected behavior

Given a permanent setting, clicking 'Apps' goes to the apps installed (as in v28),
with "Discover" either hidden or appearing lower down the list.

Installation method

None

Nextcloud Server version

29.0.4

Operating system

None

PHP engine version

None

Web server

None

Database engine version

None

Is this bug present after an update or on a fresh install?

Upgraded to a MAJOR version (ex. 28 to 29)

Are you using the Nextcloud Server Encryption module?

None

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

No response

List of activated Apps

No response

Nextcloud Signing status

No response

Nextcloud Logs

No response

Additional info

No response

Start by tracing the Apps menu entry to the /settings/apps/discover route and compare it with the installed-apps page described in the report. Determine how a permanent default should choose or hide Discover, then verify that opening Apps reaches the selected page and that Discover remains available as intended.