`haddock-autolink` submodule: Licensing, inclusion

While cloning the main ghc repository (using `git clone https://gitlab.haskell.org/ghc/ghc.git --recurse-submodules`) I noticed that the `containers` repository was being cloned. That's OK because the `containers` library is a submodule of the ghc repo.

However, I noticed that the `haddock-autolink` submodule of `containers` is also being cloned. This is because `haddock-autolink` is a submodule of the `containers` repo.

```
[submodule "containers/docs/_extensions/haddock-autolink"]
path = containers/docs/_extensions/haddock-autolink
url = https://github.com/m-renaud/haddock-autolink
```
( https://github.com/haskell/containers/blob/b216597c83755131aac0f335744e2f803eaa9399/.gitmodules )

Here is what I noticed:
- The linked submodule https://github.com/m-renaud/haddock-autolink does not have a LICENSE (or equivalent) of any sort. Should `containers` require a license given that `ghc` uses `containers` which in turn uses `haddock-autolink` ?
- All the submodules of ghc look to be hosted at https://gitlab.haskell.org/ghc/ . `haddock-autolink` seems to be a notable exception. Might it be a good idea to incorporate this submodule into the `containers` repo itself? (especially because it is a small one). Ideally all the source dependencies of ghc should be more firmly in its control so we don't need to worry about the long term availability/maintenance of the `haddock-autolink` repo which is under control of a different entity than ghc presumably.

Request maintainers of `containers` suggest if any of these two issues need to be addressed.

cc: @m-renaud