Implement dump for IKeystoreMaintenance

Sample output on Cuttlefish:

```
keystore2 running

Device info for r#TRUSTED_ENVIRONMENT with Uuid([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1])
  HAL version:              300
  Implementation name:      Rust reference implementation
  Implementation author:    Google
  Timestamp token required: false

Database size information (in bytes):
  r#DATABASE                              :        77824
  r#KEY_ENTRY                             :         4096 (unused 3603)
  r#KEY_ENTRY_ID_INDEX                    :         4096 (unused 3969)
  r#KEY_ENTRY_DOMAIN_NAMESPACE_INDEX      :         4096 (unused 3820)
  r#BLOB_ENTRY                            :         4096 (unused 863)
  r#BLOB_ENTRY_KEY_ENTRY_ID_INDEX         :         4096 (unused 3954)
  r#KEY_PARAMETER                         :         4096 (unused 2459)
  r#KEY_PARAMETER_KEY_ENTRY_ID_INDEX      :         4096 (unused 3024)
  r#KEY_METADATA                          :         4096 (unused 3826)
  r#KEY_METADATA_KEY_ENTRY_ID_INDEX       :         4096 (unused 3999)
  r#GRANT                                 :         4096 (unused 4088)
  r#AUTH_TOKEN                            :            0
  r#BLOB_METADATA                         :         4096 (unused 3572)
  r#BLOB_METADATA_BLOB_ENTRY_ID_INDEX     :         4096 (unused 3906)

```

Test: adb shell dumpsys android.security.maintenance
Bug: 344987718
Flag: android.security.keystore2.enable_dump
Change-Id: I231079f32648e2fab7fed4857f6d3e29755b0d19
diff --git a/keystore2/aconfig/flags.aconfig b/keystore2/aconfig/flags.aconfig
index 05dae46..ff817b7 100644
--- a/keystore2/aconfig/flags.aconfig
+++ b/keystore2/aconfig/flags.aconfig
@@ -26,6 +26,14 @@
 }
 
 flag {
+  name: "enable_dump"
+  namespace: "hardware_backed_security"
+  description: "Include support for dump() on the IKeystoreMaintenance service"
+  bug: "344987718"
+  is_fixed_read_only: true
+}
+
+flag {
   name: "import_previously_emulated_keys"
   namespace: "hardware_backed_security"
   description: "Include support for importing keys that were previously software-emulated into KeyMint"