[FrameworkBundle] Added dirname option to AssetsInstallCommand

I added an option to the `assets:install` command to specify the directory name you want the assets installed (`bundles` was hardcoded).

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | 
| License       | MIT
| Doc PR        |