Allow extending Symfony DI in surf

[Scarbous]

• Please check if the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

This PR add the feature to use the symfony DI in custom surf extensions.
I was not able to use the logger in my custom Task. So I decided to make surf extendable.
Just create a Extension which extends TYPO3\Surf\Cli\Symfony\DependencyInjection\Extension
create a composer package with the "type": "typo3-surf-exstension" and define the extension namespace at extra.typo3-surf.extension.

• What is the current behavior? (You can also link to an open issue here)
  I cant use for example the logger in my custom task.

• What is the new behavior (if this is a feature change)?
  The Symfony DI can get used, for example, in custom tasks.

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
  No

• Other information:

[simonschaufi]

Thank you for your contribution. Please make sure that all tests are green.

Please also write documentation how DI can be used specifically with code examples.