feat: Update Dockerfile of Thumbor to install opencv

[rrchai]

• Partial work to address [Feature] Fit org logos into the round avatar #1955

Note
"The default beeyev/thumbor-s3:7.4-alpine image does not include the opencv package, which is required for smart detection. This PR is being created to document the work to install opencv in the image, and it will be closed soon."

Below config is also added to .env just in case, but I think it's default.

DETECTORS=['thumbor.detectors.feature_detector','thumbor.detectors.face_detector']

[tschaffter]

@rrchai This post-task documentation work could have been done directly in the ticket instead of opening and closing a PR, which triggers CI workflows.

RUN apk update \
    && apk --no-cache --update add build-base 
RUN pip install --upgrade pip \
    && pip install scikit-build cmake \
    && pip install --no-use-pep517 opencv-python --no-cache-dir