Pass GitHub access token when accessing raw.githubusercontent.com in case of private recipes

[aivus]

I'm checking how to use private symfony recipes and found that symfony/flex is not using GH access token when accessing raw.githubcontent.com.

For a public repositories it's not a case, but for private repositories it's not possible to access the recipe template url from raw.githubcontent.com without using access token.

Adding access token for requests to api.github.com is covered by Composer, but it doesn't cover downloading files from raw.githubcontent.com.

This PR introduces logic for adding token for requests to raw.githubcontent.com in the similar way as composer does for api.github.com.

Limitations:

• Current implementation adds the token (if it presents) to ALL requests to the raw.githubusercontent.com, but I don't think that it's a big issue actually.

[nicolas-grekas]

Why don't you use api.github.com for private recipes?

[aivus]

2 points here:

• Rate limitations (Hit raw.githubusercontent.com to work around rate limiting #834)
• Re-use existing recipes-checker tool to build recipe

[stof]

Passing the token solves the rate limiting problem (as the rate limit is much higher for authenticated requests: https://docs.github.com/en/rest/overview/resources-in-the-rest-api#rate-limiting)

[aivus]

Ok, let's close this PR then as after forking recipes-checker and reverting changes to use api.github.com it works fine for private repos.

My idea initially was to use original recipes-checker for own private/public repos, but it seems some changes are required on checker side besides URLs.

[nicolas-grekas]

I'd be happy to make the recipe-checker a bit more generic if you're up for a PR.

[nicolas-grekas]

Thank you @aivus.