Support for Apache Server dry run on `httpd.conf`

[gzurl]

Depending on the configuration, during the boot up, Apache Server performs a dry-run over httpd.conf and then if everything went well then executes a second pass over httpd.conf.

A dry run for Apache Server means directives are invoked but they shouldn't have any effect. Currently, we do not support this in mod_wasm.c, and the side effect is the next warning:

./httpd -X
[Thu Nov 17 11:51:04.318334 2022] [wasm:notice] [pid 13747:tid 281472847323168]
[Thu Nov 17 11:51:04.318630 2022] [so:warn] [pid 13747:tid 281472847323168] AH01574: module wasm_module is already loaded, skipping`

As a consequence, wasm_runtime is also trying to load Wasm modules twice. In this case, either 1) mod_wasm emits a "Wasm module already loaded" warning message, or 2) we turn off that check and then we cannot really identify such a doubled-load scenario.

While this is not supported, the doubled-load check in pub fn from_file() in module.rs won't emit any warning.