fix(config): Decrypt sensitive appconfigs when requested

[nickvergessen]

occ config:app:set spreed recording_servers --value '{"secret":"abc"}' --sensitive

Before

occ config:list spreed --private
{
    "apps": {
        "spreed": {
…
            "recording_servers": "$AppConfigEncryption$bf2f2eea60075e78a26e608f9eef90b750c8205eddd4e15cc968569af7ae78a3|55aaf290e56e56494cb8cc0b827c121a|61442de1d928f0ad2eeff1c74bd608f6ef18dac87ab7f39075fffdbdc3d10797cf02ce2f2e604bdf775d7add6584721b0d63ba4b0e2696d3fdf94e1659366bb6|3",
…
        }
    }
}

occ config:list spreed
{
    "apps": {
        "spreed": {
…
            "recording_servers": "***REMOVED SENSITIVE VALUE***",
…
        }
    }
}

After

occ config:list spreed --private
{
    "apps": {
        "spreed": {
…
            "recording_servers": "{\"secret\":\"abc\"}",
…
        }
    }
}

occ config:list spreed
{
    "apps": {
        "spreed": {
…
            "recording_servers": "***REMOVED SENSITIVE VALUE***",
…
        }
    }
}

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)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI