docs: document the following functions with examples

* `dispatch_http_call()`
* `on_http_call_response()``
* `on_vm_start()`
* `get_vm_configuration()`
* `on_configure()`
* `get_plugin_configuration()`
* `set_tick_period()`
* `on_tick()`
* `on_http_request_headers()`
* `get_http_request_headers()`
* `get_http_request_header()`
* `add_http_request_header()`
* `resume_http_context()`
* `send_http_response()`

Author: antonengelhardt