fix(occ): Fix autocompletion of config:app:* commands

[nickvergessen]

Before

occ config:app:get spreed An unhandled exception has been thrown:
Error: Call to a member function getAppKeys() on null in /…/server/core/Command/Config/App/Base.php:31
Stack trace:
#0 /…/server/3rdparty/stecman/symfony-console-completion/src/CompletionHandler.php(299): OC\Core\Command\Config\App\Base->completeArgumentValues('...', Object(Stecman\Component\Symfony\Console\BashCompletionvironmentCompletionContext))
#1 /…/server/3rdparty/stecman/symfony-console-completion/src/CompletionHandler.php(122): Stecman\Component\Symfony\Console\BashCompletion\CompletionHandler->completeForCommandArguments()
#2 /…/server/3rdparty/stecman/symfony-console-completion/src/CompletionCommand.php(184): Stecman\Component\Symfony\Console\BashCompletion\CompletionHandler->runCompletion()
#3 /…/server/3rdparty/stecman/symfony-console-completion/src/CompletionCommand.php(123): Stecman\Component\Symfony\Console\BashCompletion\CompletionCommand->runCompletion()
#4 /…/server/3rdparty/symfony/console/Command/Command.php(326): Stecman\Component\Symfony\Console\BashCompletion\CompletionCommand->execute(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#5 /…/server/3rdparty/symfony/console/Application.php(1078): Symfony\Component\Console\Command\Command->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#6 /…/server/3rdparty/symfony/console/Application.php(324): Symfony\Component\Console\Application->doRunCommand(Object(Stecman\Component\Symfony\Console\BashCompletion\CompletionCommand), Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#7 /…/server/3rdparty/symfony/console/Application.php(175): Symfony\Component\Console\Application->doRun(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#8 /…/server/lib/private/Console/Application.php(187): Symfony\Component\Console\Application->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#9 /…/server/console.php(87): OC\Console\Application->run(Object(Symfony\Component\Console\Input\ArgvInput))
#10 /…/server/occ(33): require_once('...')
#11 {main}

After

occ config:app:get spreed 
enabled                        installed_version              signaling_dev                  signaling_token_privkey_es256  sip_bridge_dialin_info         sip_dialout
federation_enabled             recording_servers              signaling_servers              signaling_token_pubkey_es256   sip_bridge_shared_secret       types

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[nickvergessen]

/backport to stable31

[nickvergessen]

/backport to stable30

[nickvergessen]

/backport to stable29