Add log level check before logging persistent container warning

[Copilot]

Description

Adds IsEnabled(LogLevel.Warning) guard before logging in WarnPersistentContainersWithoutUserSecrets to avoid unnecessary string formatting overhead when warning level is disabled.

// Before
logger.LogWarning(MessageStrings.PersistentContainerWithoutUserSecrets, resource.Name);

// After
if (logger.IsEnabled(LogLevel.Warning))
{
    logger.LogWarning(MessageStrings.PersistentContainerWithoutUserSecrets, resource.Name);
}

This aligns with the logging pattern used throughout the codebase (e.g., AuxiliaryBackchannelRpcTarget, DashboardEventHandlers).

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
    • If yes, did you have an API Review for it?
      • Yes
      • No
    • Did you add <remarks /> and <code /> elements on your triple slash comments?
      • Yes
      • No
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
    • If yes, have you done a threat model and had a security review?
      • Yes
      • No
  • No
• Does the change require an update in our Aspire docs?
  • Yes
    • Link to aspire.dev issue:
      • New issue
  • No

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