[Process] Add Process::disableOutput and Process::enableOutput methods

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #9007
| License       | MIT
| Doc PR        | https://github.com/symfony/symfony-docs/pull/3664

This is another implementation for #9007 that allows to disable the output/error-output storage in a Process in order to avoid using memory.
This is particularly useful when the process outputs large data and it's not read.