Do not make calls to Packagist when creating `Projects`

[franmomu]

I wanted to try some commands and took some time to just show the command list and that's because:

dev-kit/src/Config/Projects.php

Lines 35 to 52 in d9010be

	public function __construct(PackagistClient $packagist)
	{
	$this->packagist = $packagist;
	$processor = new Processor();
	$projectsConfigs = $processor->processConfiguration(new ProjectsConfiguration(), [
	'sonata' => ['projects' => Yaml::parseFile(__DIR__.'/../../config/projects.yaml')],
	]);
	foreach ($projectsConfigs['projects'] as $name => $config) {
	$package = $this->packagist->get(sprintf(
	'sonata-project/%s',
	$name
	));
	$this->projects[$name] = Project::fromValues($name, $config, $package);
	}
	}

When instantiating is making several calls to packagist.

[OskarStark]

We should keep the calls, but maybe cache the response for some time

[franmomu]

I meant to make the calls only when needed (and also caching), not when instantiating.

[VincentLanglet]

In a similar way, it would be nice to do the same for the PR on the github api.
#1563 (comment)

We're doing $this->githubPager->fetchAll($this->github->search(), 'issues', [$query->toString()]) then a call to the api by PR. It could be done only when some extra information are needed.