Enhance HTTPserver to support nginx-like header vars and build-in backend pool (#1497)

* HTTPServer: Support set headers with nginx-like vars

* HTTPServer: test nginx-like vars

* HTTPServer: Implement backendPool with generating proxy pipeline

* Support labels for metadata of object

* Add httpserver owner label and fix unittest

* Fix Validate of validator spec

* Use cluster to manage generated pipeline instead traffic controller

* Forbid updating generated objects

* Update quick start to adopt backend pool in HTTPServer

* Doc: Add nginx header vars

* Doc: Update header size

* Fix unit tests

* Fix TestPathValidate

Author: xxx7xxxx

docs/01.Getting-Started/1.1.Quick-Start.md

@@ -2,11 +2,10 @@
 
 The basic usage of Easegress is to quickly set up a proxy for the backend servers.
 
-### Launch Easegress
+## Launch Easegress
 
 Easegress can be installed from pre-built binaries or from source. For details, see [Install](1.2.Install.md).
 
-
 Then we can execute the server:
 
 ```bash
@@ -17,7 +16,7 @@ $ easegress-server
 
 By default, Easegress opens ports 2379, 2380, and 2381; however, you can modify these settings along with other arguments either in the configuration file or via command-line arguments. For a complete list of arguments, please refer to the `easegress-server --help` command.
 
-After launching successfully, we could check the status of the one-node cluster. 
+After launching successfully, we could check the status of the one-node cluster.
 
 ```bash
 $ egctl get member
@@ -27,40 +26,72 @@ $ egctl describe member
 ...
 ```
 
-### Reverse Proxy
+## Reverse Proxy
 
 Assuming you have two backend HTTP services running at `127.0.0.1:9095` and `127.0.0.1:9096`, you can initiate an HTTP proxy from port 10080 to these backends using the following command:
 
 ```bash
-$ egctl create httpproxy demo --port 10080 \ 
+$ egctl create httpproxy demo --port 10080 \
   --rule="/pipeline=http://127.0.0.1:9095,http://127.0.0.1:9096" \
   --rule="/prefix*=http://127.0.0.1:9097"
 ```
 
 Then try it:
+
 ```bash
-$ curl -v 127.0.0.1:10080/pipeline
+curl -v 127.0.0.1:10080/pipeline
 ```
 
 The request will be forwarded to either `127.0.0.1:9095/pipeline` or `127.0.0.1:9096/pipeline`, utilizing a round-robin load-balancing policy.
 
 ```bash
-$ curl -v 127.0.0.1:10080/prefix/123
+curl -v 127.0.0.1:10080/prefix/123
 ```
-The request will be forwarded to `127.0.0.1:9097/prefix/123`. 
 
+The request will be forwarded to `127.0.0.1:9097/prefix/123`.
+
+## YAML Configuration
 
-### YAML Configuration
+The `egctl create httpproxy` command is convenient, but for production use, you'll want more control. Easegress uses two main resources: **HTTPServer** (handles incoming requests) and **Pipeline** (processes and routes requests).
 
-The `egctl create httpproxy` command mentioned above is actually syntactic sugar; it creates two Easegress resources under the hood: `HTTPServer` and `Pipeline`.
+### Method 1: HTTPServer with Built-in Backend Pool
 
-Now let's create them using yaml files:
+This approach automatically creates pipelines for you:
+
+```bash
+$ echo 'kind: HTTPServer
+name: demo-backend-pool
+port: 10080
+https: false
+rules:
+  - paths:
+    - pathPrefix: /demo0
+      backendPool:
+        loadBalance:
+          policy: roundRobin
+        servers:
+            - url: http://127.0.0.1:9091
+            - url: http://127.0.0.1:9092
+    - pathPrefix: /demo1
+      backendPool:
+        loadBalance:
+          policy: roundRobin
+        servers:
+            - url: http://127.0.0.1:9093
+            - url: http://127.0.0.1:9094' | egctl create -f -
+```
+
+It will generate one pipeline for each backendPool. For example, `demo-backend-pool` generates pipeline`GENERATED-demo-backend-pool-0-0` and `GENERATED-demo-backend-pool-0-1` which couldn't be updated or deleted via `egctl` (User APIs).
+
+### Method 2: HTTPServer with Separate Pipelines
+
+Create HTTPServer:
 
 ```bash
 $ echo '
 kind: HTTPServer
-name: demo
-port: 10080
+name: demo-backend
+port: 10081
 https: false
 rules:
   - paths:
@@ -69,7 +100,8 @@ rules:
     - pathPrefix: /prefix
       backend: demo-1 ' | egctl create -f -
 ```
-More details about [HTTPServer](../02.Tutorials/2.2.HTTP-Proxy-Usage.md).
+
+Create the Pipelines:
 
 ```bash
 $ echo '
@@ -98,7 +130,7 @@ filters:
     - servers:
       - url: http://127.0.0.1:9097' | egctl create -f -
 ```
+
 More details about [Pipeline](../02.Tutorials/2.3.Pipeline-Explained.md).
 
 You can also modify, update, or delete these resources using `egctl`; for more details, refer to the [egctl usage](../02.Tutorials/2.1.egctl-Usage.md) guide.
-