install: rename --dev-only to --only-dev

This aligns option to existing options like --no-dev and --no-root.

Relates-to: python-poetry#2917

docs/docs/cli.md

@@ -129,10 +129,10 @@ poetry install --no-dev
 ```
 
 Conversely, you can specify to the command that you only want to install the development dependencies
-by passing the `--dev-only` option. Note that `--no-dev` takes priority if both options are passed.
+by passing the `--only-dev` option. Note that `--no-dev` takes priority if both options are passed.
 
 ```bash
-poetry install --dev-only
+poetry install --only-dev
 ```
 
 If you want to remove old dependencies no longer present in the lock file, use the
@@ -168,13 +168,13 @@ If you want to skip this installation, use the `--no-root` option.
 poetry install --no-root
 ```
 
-Installation of your project's package is also skipped when the `--dev-only`
+Installation of your project's package is also skipped when the `--only-dev`
 option is passed.
 
 ### Options
 
 * `--no-dev`: Do not install dev dependencies.
-* `--dev-only`: Only install dev dependencies.
+* `--only-dev`: Only install dev dependencies.
 * `--no-root`: Do not install the root package (your project).
 * `--dry-run`: Output the operations but do not execute anything (implicitly enables --verbose).
 * `--remove-untracked`: Remove dependencies not presented in the lock file

poetry/console/commands/install.py

@@ -10,7 +10,7 @@ class InstallCommand(InstallerCommand):
 
     options = [
         option("no-dev", None, "Do not install the development dependencies."),
-        option("dev-only", None, "Only install the development dependencies."),
+        option("only-dev", None, "Only install the development dependencies."),
         option(
             "no-root", None, "Do not install the root package (the current project)."
         ),
@@ -67,7 +67,7 @@ def handle(self) -> int:
 
         self._installer.extras(extras)
         self._installer.dev_mode(not self.option("no-dev"))
-        self._installer.dev_only(self.option("dev-only"))
+        self._installer.dev_only(self.option("only-dev"))
         self._installer.dry_run(self.option("dry-run"))
         self._installer.remove_untracked(self.option("remove-untracked"))
         self._installer.verbose(self._io.is_verbose())
@@ -77,7 +77,7 @@ def handle(self) -> int:
         if return_code != 0:
             return return_code
 
-        if self.option("no-root") or self.option("dev-only"):
+        if self.option("no-root") or self.option("only-dev"):
             return 0
 
         try: