docker: simplify duniter subcommand run

When the first argument of the entrypoint is not an option or is '--' then bypass the default configuration via environment variables and directly run duniter with the given parameters (after removing the first one when it is '--').

The affected scripts and documentation were updated.

docker/README.md

@@ -81,23 +81,10 @@ You can pass any other option to duniter using the `command` docker-compose elem
       - "--wasm-execution=interpreted-i-know-what-i-do"
 ```
 
-# Running duniter subcommands
+# Running duniter subcommands or custom set of options
 
-You can run any duniter subcommand this way:
-```
-$ docker run --rm duniter/duniter-v2s:latest <subcommand> ...
-```
-
-For example to generate a key:
-```
-$ docker run --rm duniter/duniter-v2s:latest key generate
-```
-
-In this case the `DUNITER_*` environment variables are ignored.
-
-# Running custom duniter options
-
-To test duniter from the command line without the default configuration detailed in the "Environment variables" section use `--` as the first argument. For example:
+To run duniter from the command line without the default configuration detailed in the "Environment variables" section use `--` as the first argument. For example:
 ```
+$ docker run --rm duniter/duniter-v2s:latest -- key generate
 $ docker run --rm duniter/duniter-v2s:latest -- --chain gdev ...
 ```