feat(plugin): add proxywasm plugin (#284)

* feat(plugin): add `proxywasm` plugin

The `proxywasm` plugin is a WASM Filter following the ProxyWasm ABI Specification using the proxywasm go sdk

This allows extensibility with any reverse proxy who implements the ProxyWasm ABI Specification.

The current WASM Filter was successfully tested with APISIX, Envoy, Nginx with ngx_wasm_module from Kong and Istio.

Fixes #145

docs/plugins/apacheapisix.md

@@ -0,0 +1,33 @@
+# Apache APISIX Plugin
+
+The Apache APISIX Plugin is a WASM Plugin written with the Proxy Wasm SDK.
+
+## Provider compatibility grid
+
+| Provider                                | Dynamic | Blocking |
+|-----------------------------------------|:-------:|:--------:|
+| [Docker](/providers/docker)             |    ✅    |    ✅     |
+| [Docker Swarm](/providers/docker_swarm) |    ❓    |    ❓     |
+| [Kubernetes](/providers/kubernetes)     |    ❓    |    ❓     |
+
+## Install the plugin to Apache APISIX
+
+```yaml
+wasm:
+  plugins:
+    - name: proxywasm_sablier_plugin
+      priority: 7997
+      file: /wasm/sablierproxywasm.wasm # Downloaded WASM Filter path
+```
+
+## Configuration
+
+You can have the following configuration:
+
+```yaml
+routes:
+  - uri: "/"
+    plugins:
+      proxywasm_sablier_plugin:
+        conf: '{ "sablier_url": "sablier:10000", "group": ["my-group"], "session_duration": "1m", "dynamic": { "display_name": "Dynamic Whoami" } }'
+```