[llvm] [CI][Github] Add Fully Qualified Container Names to Best Practices (PR #165067)

[Baranov Victor via llvm-commits]

vbvictor wrote:

By the way, it seems that `CIBestPractices.rst` in unreachable via normal link-jumps in the web.
Here it is under "hidden" https://github.com/llvm/llvm-project/blob/7be3cac735b272ffa9b89e36c8c7b7a5d333cf40/llvm/docs/Reference.rst?plain=1#L19

But it doesn't have a dedicated entry in "Additional topics":

https://github.com/llvm/llvm-project/blob/7be3cac735b272ffa9b89e36c8c7b7a5d333cf40/llvm/docs/Reference.rst?plain=1#L175

https://github.com/llvm/llvm-project/pull/165067