egctl proposal (#797)

* add egctl proposal

Signed-off-by: zirain <zirain2009@gmail.com>

* Update docs/latest/design/egctl.md

Co-authored-by: Arko Dasgupta <arkodg@users.noreply.github.com>
Signed-off-by: zirain <hejianpeng2@huawei.com>

* udpate arkodg's review comments

Signed-off-by: hejianpeng <hejianpeng2@huawei.com>

* address comment and update config command

Signed-off-by: hejianpeng <hejianpeng2@huawei.com>

* update wording

Signed-off-by: hejianpeng <hejianpeng2@huawei.com>

* update review comments

Signed-off-by: hejianpeng <hejianpeng2@huawei.com>

* fix typo

Signed-off-by: hejianpeng <hejianpeng2@huawei.com>

* update dane's comment

Signed-off-by: hejianpeng <hejianpeng2@huawei.com>

* remove install/uninstall

Signed-off-by: hejianpeng <hejianpeng2@huawei.com>

* remove egctl log command

Signed-off-by: hejianpeng <hejianpeng2@huawei.com>

Signed-off-by: zirain <zirain2009@gmail.com>
Signed-off-by: zirain <hejianpeng2@huawei.com>
Signed-off-by: hejianpeng <hejianpeng2@huawei.com>
Co-authored-by: Arko Dasgupta <arkodg@users.noreply.github.com>

docs/latest/design/egctl.md

@@ -0,0 +1,56 @@
+# Introduce egctl
+
+## Motivation
+
+EG should provide a command line tool with following capabilities:
+
+- Collect configuration from envoy proxy and gateway
+- Analyse system configuration to diagnose any issues in envoy gateway
+
+This tool is named `egctl`.
+
+## Syntax
+
+Use the following syntax to run `egctl` commands from your terminal window:
+
+```console
+egctl [command] [entity] [name] [flags]
+```
+
+where `command`, `name`, and `flags` are:
+
+* `command`: Specifies the operation that you want to perform on one or more resources,
+  for example `config`, `version`.
+
+* `entity`: Specifies the entity the operation is being performed on such as `envoy-proxy` or `envoy-gateway`.
+
+* `name`: Specifies the name of the specified instance. 
+
+* `flags`: Specifies optional flags. For example, you can use the `-c` or `--config` flags to specify the values for installing.
+
+If you need help, run `egctl help` from the terminal window.
+
+## Operation
+
+The following table includes short descriptions and the general syntax for all the `egctl` operations:
+
+| Operation | Syntax                           | Description                                                                 |
+| --------- | -------------------------------- | --------------------------------------------------------------------------- |
+| `version` | `egctl version`                  | Prints out build version information.                                       |
+| `config`  | `egctl config ENTITY`            | Retrieve information about proxy configuration from envoy proxy and gateway |
+| `analyze` | `egctl analyze`                  | Analyze EG configuration and print validation messages                      |
+
+## Examples
+
+Use the following set of examples to help you familiarize yourself with running the commonly used `egctl` operations:
+
+```console
+# Retrieve all information about proxy configuration from envoy
+egctl config envoy-proxy all <instance_name>
+
+# Retrieve listener information about proxy configuration from envoy 
+egctl config envoy-proxy listener <instance_name>
+
+# Retrieve information about envoy gateway
+egctl config envoy-gateway
+```