refactor: standardize command naming

This standardization makes it somewhat easier to read stacktraces as the command names are all uniform, so it will be slightly easier to scan trace output.

docs/development/plugin-creation.md

@@ -233,7 +233,7 @@ set -eo pipefail
 [[ $DOKKU_TRACE ]] && set -x
 source "$PLUGIN_CORE_AVAILABLE_PATH/common/functions"
 
-hello_main_cmd() {
+cmd-hello-default() {
   declare desc="prints Hello \$APP"
   declare cmd="hello" argv=("$@")
   [[ ${argv[0]} == "$cmd" ]] && shift 1
@@ -250,7 +250,7 @@ hello_main_cmd() {
   echo "Hello $APP"
 }
 
-hello_main_cmd "$@"
+cmd-hello-default "$@"
 ```
 
 `hello/subcommands/world`
@@ -261,7 +261,7 @@ set -eo pipefail
 [[ $DOKKU_TRACE ]] && set -x
 source "$PLUGIN_CORE_AVAILABLE_PATH/common/functions"
 
-hello_world_cmd() {
+cmd-hello-world() {
   declare desc="prints Hello world"
   declare cmd="hello:world" argv=("$@")
   [[ ${argv[0]} == "$cmd" ]] && shift 1
@@ -269,7 +269,7 @@ hello_world_cmd() {
   echo "Hello world"
 }
 
-hello_world_cmd "$@"
+cmd-hello-world "$@"
 ```
 
 `hello/commands`