T6934: Add preshared key for zabbix-agent monitoring service

- Allow configure preshared key for zabbix-agent
- Added op mode command for generatre random psk secret
- Removed duplicate xml definition for psk settings


Configure authentication mode:
```
# set service monitoring zabbix-agent authentication mode
Possible completions:
   pre-shared-secret    Use a pre-shared secret key
```

Configure PSK Settings:
```
# set service monitoring zabbix-agent authentication psk
Possible completions:
   id                   ID for authentication
   secret               pre-shared secret key

```

Generate Random PSK:
```
$ generate psk random
Possible completions:
  <Enter>               Execute the current command
  size                  Key size in bytes

```

1 files changed, 45 insertions, 0 deletions

diff --git a/src/op_mode/generate_psk.py b/src/op_mode/generate_psk.py
new file mode 100644
index 000000000..d51293712
--- /dev/null
+++ b/src/op_mode/generate_psk.py
@@ -0,0 +1,45 @@
+#!/usr/bin/env python3
+#
+# Copyright (C) 2024 VyOS maintainers and contributors
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 or later as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+import argparse
+
+from vyos.utils.process import cmd
+
+
+def validate_hex_size(value):
+    """Validate that the hex_size is between 32 and 512."""
+    try:
+        value = int(value)
+    except ValueError:
+        raise argparse.ArgumentTypeError("hex_size must be integer.")
+
+    if value < 32 or value > 512:
+        raise argparse.ArgumentTypeError("hex_size must be between 32 and 512.")
+    return value
+
+
+if __name__ == '__main__':
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        "--hex_size",
+        type=validate_hex_size,
+        help='PKS value size in hex format. Default is 32 bytes.',
+        default=32,
+
+        required=False,
+    )
+    args = parser.parse_args()
+
+    print(cmd(f'openssl rand -hex {args.hex_size}'))
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