Build-image: Feature request: webp support

[rjvdw]

In the build image for Ubuntu 16, the provided version of ImageMagick does not have webp support. From what I understand, it is relatively simple to add support for webp: https://askubuntu.com/a/788917

Could you consider doing this?

[samheather]

+1 yes please. webp support is a top request for us - it's a major component of Google Page Speed Insights, and handling it at application is sub-optimal.

[jacintoArias]

We definetly need this, this discussion seems to be asking for almost the same
https://github.com/netlify/build-image/issues/157

[dancingmonkey]

Please!!! add this. 2020 :)