Add build script

[victorpopkov]

Problem

Similar to dstmodders/docker-imagemagick#18:

Even though it's not a big deal to run four commands to build images locally, it would be nice to have a script for convenience.

Proposed solution

Implement a script named bin/build.sh to automate building images locally (see dstmodders/docker-imagemagick#18) with Docker CLI and daemon checks (see dstmodders/docker-imagemagick#41).

Progress

• Create the build.sh script in the bin directory.
• Add a check for the Docker CLI and print an error if it's missing.
• Add a check for the Docker daemon and print an error if it’s not running.
• Create build() to run either docker build or docker buildx build based on availability.
• Add support for choosing which images to build: all, latest or official.
• Add support for -b, --build-cpus flag that sets --build-arg BUILD_CPUS.
• Add support for -p, --progress [auto|plain|tty|rawjson] flag.