Enable WEBP support

[Flow86]

Enable WEBP support in GD module, so that processing webp files in nextcloud will work.

I created a small app https://github.com/Flow86/preview_webp to allow preview of webp files in nextcloud file browser.

[J0WI]

This is a tricky one. Normally we use example Dockerfiles to support additional apps.
But in this case we can't extend the already compiled GD extension.

I just asked for upstream support in nextcloud/server#13552 (comment). @tilosp would you agree to extend the GD extension for WebP support?

[J0WI]

Please also add the corresponding dependency to the Alpine variant:

docker/Dockerfile-alpine.template

Line 35 in 4a94550

docker-php-ext-configure gd --with-freetype-dir=/usr --with-png-dir=/usr --with-jpeg-dir=/usr; \

[Flow86]

Please also add the corresponding dependency to the Alpine variant

Done in 11cc51e

[tilosp]

@tilosp would you agree to extend the GD extension for WebP support?

yes adding support for WebP is fine, especially since it only adds <1MB.

[J0WI]

Thanks!