Add SymfonyHttpClient file configuration

[nlemoine]

Unfortunately, current implementation does not allow to use SymfonyHttpClient in the config file.

This PR decouples the http object creation logic from the config parsing.

However, there's still some inconsistencies because Config object properties and cli/file parameters are being merged/mixed up/not consistently named (temp_dir / webAllowInsecure).

[nlemoine]

Maybe bringing a private method like getConfigOrParameter with parameter taking precedence over config file value would solve this?

[gordalina]

Thank you for your contribution! Released in 6.3.0

[nlemoine]

Thanks!