docs: translate the document of request block plugin to English. (#150)

plugins/wasm-cpp/extensions/request_block/README_EN.md

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+<p>
+   English | <a href="README.md">中文</a>
+</p>
+
+# Description
+`request-block` plugin implements a request blocking function based on request characteristics such as URL and request header. It can be used to protect internal resources from unauthorized access.
+
+# Configuration Fields
+
+| Name | Type | Requirement |  Default Value | Description |
+| -------- | -------- | -------- | -------- | -------- |
+|  block_urls     |  array of string     | Optional. Choose one from following: `block_urls`, `block_headers`, `block_bodies` |  -  |  HTTP URLs to be blocked. |
+|  block_headers     |  array of string     | Optional. Choose one from following: `block_urls`, `block_headers`, `block_bodies` |  -  |  HTTP request headers to be blocked.  |
+|  block_bodies     |  array of string     | Optional. Choose one from following: `block_urls` ,`block_headers`, `block_bodies` |  -  |  HTTP request bodies to be blocked.  |
+|  blocked_code     |  number     |  Optional     |   403  |  HTTP response status code to be sent when corresponding request is blocked.  |
+|  blocked_message     |  string     |  Optional   |   -  |  HTTP response body to be sent when corresponding request is blocked.   |
+|  case_sensitive     |  bool     |  Optional     |   true  |  Whether to use case-senstive comparison when matching. Enabled by default.   |
+
+# Configuration Samples
+
+## Block Specific Request URLs
+```yaml
+block_urls:
+- swagger.html
+- foo=bar
+case_sensitive: false
+```
+
+According to the configuration above, following requests will be blocked:
+
+```bash
+curl http://example.com?foo=Bar
+curl http://exmaple.com/Swagger.html
+```
+
+## Block Specific Request Headers
+```yaml
+block_headers:
+- example-key
+- example-value
+```
+
+According to the configuration above, following requests will be blocked:
+
+```bash
+curl http://example.com -H 'example-key: 123'
+curl http://exmaple.com -H 'my-header: example-value'
+```
+
+## Block Specific Request Bodies
+```yaml
+block_bodies:
+- "hello world"
+case_sensitive: false
+```
+
+According to the configuration above, following requests will be blocked:
+
+```bash
+curl http://example.com -d 'Hello World'
+curl http://exmaple.com -d 'hello world'
+```
+
+## Only Enable for Specific Routes or Domains
+```yaml
+# Use _rules_ field for fine-grained rule configurations 
+_rules_:
+# Rule 1: Match by route name
+- _match_route_:
+  - route-a
+  - route-b
+  block_bodies: 
+  - "hello world"
+# Rule 2: Match by domain
+- _match_domain_:
+  - "*.example.com"
+  - test.com
+  block_urls: 
+  - "swagger.html"
+  block_bodies:
+  - "hello world"
+```
+In the rule sample of `_match_route_`, `route-a` and `route-b` are the route names provided when creating a new gateway route. When the current route names matches the configuration, the rule following shall be applied.
+In the rule sample of `_match_domain_`, `*.example.com` and `test.com` are the domain names used for request matching. When the current domain name matches the configuration, the rule following shall be applied.
+All rules shall be checked following the order of items in the `_rules_` field, The first matched rule will be applied. All remained will be ignored.
+
+# Maximum Request Body Size Limitation
+
+When `block_bodies` is configured, body matching shall only be performed when its size is smaller than 32MB. If not, and no `block_urls` or `block_headers` configuration is matched, the request won't be blocked.
+When `block_bodies` is configured, if the size of request body exceeds the global configuration of DownstreamConnectionBufferLimits, a ``413 Payload Too Large`` response will be returned.