wasm: removed automatical route refreshment and add a foreign function to clear the route cache

[wbpcode]

trafficstars

Commit Message: wasm: removed automatical route refreshment and add a foreign function to clear the route cache

Additional Description:

Here are the reasons to do this change:

1. It make it's impossible to only mofify the host or path or some headers but don't effect the route result.
2. Basically, refreshing route is not encouraged. Even the filters (ext_authz, jwt_authz, ext_proc, etc) who acutally need or want to clear the route cache will also provide a flag (and basically default to false) to control the behavior.
3. Refreshing route have big effect to the traffic and should only be done explicitly (code or configurations), we should never change it implicitly.

Risk Level: low. Testing: n/a. Docs Changes: n/a. Release Notes: n/a. Platform Specific Features: n/a.