Rename master to main

[vasilvestre]

As it is the new standard, I see no reason to do not rename it.

[artandor]

I think i did not because symfonycloud would not work with main, and some other tools aswell. But it seems that we won't need those tools at all ?

[vasilvestre]

I remember this, I think we can move safely so. Only the administrator can change the default github branch and I can't :)

[artandor]

Done