DR-765 Change code for Discovery enforcement

* Update the PAM protobuf to keeperapp-protobuf PR 106.
* Change CMT_GENERAL to CMT_DISCOVERY for any discovery gateway action.
* Added a readme on how to generate a protobuf python file.

To enable Discovey ...

```
https://dev.keepersecurity.com/console/dev2/#login

once logged in, navigate to Admin -> Roles
find the role that belongs to the user you're using
click on Enforcement Policies button
click on Privileged Access Manager tab (left side menu panel)
at the very bottom, you should see the Discovery enforcement
```

This enforcement permission via requests to the gateway.
There are still commands in Commander that can be run by
any person, which we may need to lock down.

keepercommander/commands/discover/job_remove.py

@@ -52,7 +52,7 @@ def execute(self, params, **kwargs):
                         gateway_action=GatewayActionDiscoverJobRemove(
                             inputs=action_inputs,
                             conversation_id=conversation_id),
-                        message_type=pam_pb2.CMT_GENERAL,
+                        message_type=pam_pb2.CMT_DISCOVERY,
                         is_streaming=False,
                         destination_gateway_uid_str=gateway_context.gateway_uid
                     )

keepercommander/commands/discover/job_start.py

@@ -211,7 +211,7 @@ def execute(self, params, **kwargs):
             gateway_action=GatewayActionDiscoverJobStart(
                 inputs=action_inputs,
                 conversation_id=conversation_id),
-            message_type=pam_pb2.CMT_GENERAL,
+            message_type=pam_pb2.CMT_DISCOVERY,
             is_streaming=False,
             destination_gateway_uid_str=gateway_context.gateway_uid
         )

keepercommander/commands/discover/rule_add.py

@@ -46,7 +46,7 @@ def validate_rule_statement(params: KeeperParams, gateway_context: GatewayContex
             gateway_action=GatewayActionDiscoverRuleValidate(
                 inputs=action_inputs,
                 conversation_id=conversation_id),
-            message_type=pam_pb2.CMT_GENERAL,
+            message_type=pam_pb2.CMT_DISCOVERY,
             is_streaming=False,
             destination_gateway_uid_str=gateway_context.gateway_uid
         )

keepercommander/proto/README.md

@@ -0,0 +1,42 @@
+# Protoc
+
+These files were generated with protoc 3.19.4.
+
+https://github.com/protocolbuffers/protobuf/releases/tag/v3.19.4
+
+On macOS, you will need to approve the running of `protoc`.
+This can be done by running `protoc`, approving the dialog box, then going
+  to the **Privacy & Security** tab in the **Settings**. 
+In the **Security** section, allow `protoc` to run. 
+The next time you run `protoc`, you'll still  get a popup, but it will allow 
+  the application to run.
+
+## Generate a Python file
+
+Change into the directory, of the repo, that contains the .proto files. 
+You need to be in that directory because the `.proto` file 
+  may include other `.proto` files.
+
+```shell
+/path/to/protoc-3.19.4-osx-x86_64/bin/protoc --python_out=.. FOO.proto
+```
+In the prior directory, `FOO_pb2.py` will be created. 
+Move the file into the `keepercommander/proto` directory.
+
+## Edit the file
+
+Ignore `# Generated by the protocol buffer compiler.  DO NOT EDIT!` :)
+
+You'll need change the import files to relative style imports. For example, change ....
+
+```python
+import enterprise_pb2 as enterprise_pb2
+import record_pb2 as record_pb2
+```
+
+to 
+
+```python
+from . import enterprise_pb2 as enterprise_pb2
+from . import record_pb2 as record_pb2
+```