Remove bcmath and gmp warning if WebAuthn is not used

[MichaIng]

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Is your feature request related to a problem? Please describe.
The admin panel prints a warning if bcmath and/or gmp PHP module is not available. Those two modules are (AFAIK) only required for WebAuthn. The generic "urgent" module recommendation text is misleading in this case since it does not imply any performance or compatibility issue to not have them installed, aside of an optional non-security relevant feature being not available.

Describe the solution you'd like
If I followed the isWebAuthnAvailable function correctly, the WebAuthn section is only shown with this two modules installed. I would instead like to have the WebAuthn section always shown and the "missing modules" info shown there in case. So users and admins always see this Nextcloud feature but as well see the info if and why it cannot be used. This is especially useful for shared hostings, so users can inform the hosting provider and ask to have those modules installed to make a certain feature available, instead of saying "the admin panel recommends for some generic reason".

Describe alternatives you've considered
Alternatively the admin panel could print more detailed info what this modules are required for. So admins don't need to either track the reason themselves or follow the recommendation "blindly" if even possible or ignore it without having a good feeling with this (🙂) but know exactly what those modules are for and decide well-founded.

Additional context
Relevant code:

• Admin panel checks:

  server/apps/settings/lib/Controller/CheckSetupController.php

  Lines 592 to 598 in 987f621

  	if (!extension_loaded('bcmath')) {
  	$recommendedPHPModules[] = 'bcmath';
  	}
  	if (!extension_loaded('gmp')) {
  	$recommendedPHPModules[] = 'gmp';
  	}

• WebAuthn check:

  server/lib/private/Authentication/WebAuthn/Manager.php

  Lines 260 to 274 in 9271d65

  	public function isWebAuthnAvailable(): bool {
  	if (!extension_loaded('bcmath')) {
  	return false;
  	}
  	if (!extension_loaded('gmp')) {
  	return false;
  	}
  	if (!$this->config->getSystemValueBool('auth.webauthn.enabled', true)) {
  	return false;
  	}
  	return true;
  	}

• Settings section:

  server/apps/settings/lib/Settings/Personal/Security/WebAuthn.php

  Lines 71 to 77 in b219ead

  	public function getSection(): ?string {
  	if (!$this->manager->isWebAuthnAvailable()) {
  	return null;
  	}
  	return 'security';
  	}

[szaimen]

cc @nextcloud/server-triage is this feasible?