Add HTTP3 support (experimental)

Co-authored-by: Ludovic Fernandez <ldez@users.noreply.github.com>

docs/content/reference/static-configuration/env-ref.md

@@ -102,6 +102,9 @@ Entry points definition. (Default: ```false```)
 `TRAEFIK_ENTRYPOINTS_<NAME>_ADDRESS`:  
 Entry point address.
 
+`TRAEFIK_ENTRYPOINTS_<NAME>_ENABLEHTTP3`:  
+Enable HTTP3. (Default: ```false```)
+
 `TRAEFIK_ENTRYPOINTS_<NAME>_FORWARDEDHEADERS_INSECURE`:  
 Trust all forwarded headers. (Default: ```false```)
 
@@ -174,6 +177,9 @@ plugin's GOPATH.
 `TRAEFIK_EXPERIMENTAL_DEVPLUGIN_MODULENAME`:  
 plugin's module name.
 
+`TRAEFIK_EXPERIMENTAL_HTTP3`:  
+Enable HTTP3. (Default: ```false```)
+
 `TRAEFIK_EXPERIMENTAL_KUBERNETESGATEWAY`:  
 Allow the Kubernetes gateway api provider usage. (Default: ```false```)