Moved Content Capture settings to DeviceConfig.

To test, manually played with 'adb shell device_config'. Examples:

$ adb shell device_config list content_capture
$ adb shell device_config delete content_capture enable_contentcapture
$ adb shell stop && adb shell start
$ adb shell service check content_capture
Service content_capture: not found

$ adb shell device_config put content_capture enable_contentcapture always
$ adb shell stop && adb shell start
$ adb shell service check content_capture
Service content_capture: found

Then ran CTS and FrameworkCoreTests below...

Test: atest CtsContentCaptureServiceTestCases \
      FrameworksCoreTests:android.provider.SettingsBackupTest#secureSettingsBackedUpOrBlacklisted
Test: m update-api

Bug: 121037717
Bug: 121153631

Change-Id: Ib93bf8181253228ccbdb3edbd84c5d0431c84eb4