Describe the bug
The supported operation files under /etc/tedge/operations/c8y should be ideally loaded only once on c8y-mapper startup. However, it is actually loaded many times. This can be explained by tracing how get_operations() functions are called.

1. init messages
   

   thin-edge.io/crates/extensions/c8y_mapper_ext/src/converter.rs

   Line 1278 in 0866b9b

   let supported_operations_message = self.create_supported_operations(

2. constructing CumulocityConverter
   

   thin-edge.io/crates/extensions/c8y_mapper_ext/src/converter.rs

   Line 216 in 0866b9b

   let operations = Operations::try_new(&*config.ops_dir)?;

3. registering a new command registration message (as many times as command registration messages received)
   

   thin-edge.io/crates/extensions/c8y_mapper_ext/src/converter.rs

   Line 1400 in 0866b9b

   let need_cloud_update = self.update_operations(ops_dir.as_std_path())?;

My comments:

(2) is actually redundant. Since already operations get created during init, they should parse to CumulocityConverter.

(3) is most problematic. CumulocityConverter::register_operation() is called by receiving a command registration message. It means, if user has 5 command registration messages, the supported operation directory will be loaded 5 times. I have a doubt if mapper has to load the directory every time when a command registration message arrives.

To Reproduce
Easy check is to use validation for custom operation handler. If the contents of a custom handler is invalid, it logs a warning message. This validation is called inside the get_operations() function.

Prepare the version of #3144.

1. Create a invalid custom operation handler file, e.g. /etc/tedge/operations/c8y/my_CustomOperation

[exec]
topic = "c8y/devicecontrol/notifications"
on_fragment = "com_cumulocity_model_WebCamDevice"
command_name = "/usr/bin/do_something.sh ${.payload.com_cumulocity_model_WebCamDevice.parameters}"

2. Restart c8y-mapper.
3. See the output of the c8y-mapper. You'll find 7 times of the warning message.

WARN c8y_api::smartrest::operations: ''command' is missing in the JSON custom operation handler mapping 'my_CustomOperation'

Expected behavior
The operation files should be scanned as few times as possible.

Screenshots

Environment (please complete the following information):

• OS [incl. version]
• Hardware [incl. revision]
• System-Architecture [e.g. result of "uname -a"]
• thin-edge.io version [e.g. 1.3.0]: 1.3.1

Additional context
The directory will be loaded when file change is detected, however, this should be good.