Show all defaults in help text, consolidate some

[AlanCoding]

I noticed that the default --tag was not showing up. This is very high up there on the scale of user impact, so I really want the help text to show it.

I also tried to have all options share a common pattern for printing their default value.

$ ansible-builder build --help
usage: ansible-builder build [-h] [-t TAG] [-f FILENAME] [-c BUILD_CONTEXT]
                             [--container-runtime {podman,docker}] [--build-arg BUILD_ARGS]
                             [-v {0,1,2,3}]

Creates a build context (including a Containerfile) from an execution environment spec. The build
context will be populated from the execution environment spec. After that, the specified container
runtime podman/docker will be invoked to build an image from that definition. After building the image,
it can be used locally or published using the supplied tag.

optional arguments:
  -h, --help            show this help message and exit
  -t TAG, --tag TAG     The name for the container image being built (default: ansible-execution-
                        env:latest)
  -f FILENAME, --file FILENAME
                        The definition of the execution environment (default: execution-environment.yml)
  -c BUILD_CONTEXT, --context BUILD_CONTEXT
                        The directory to use for the build context (default: context)
  --container-runtime {podman,docker}
                        Specifies which container runtime to use (default: podman)
  --build-arg BUILD_ARGS
                        Build-time variables to pass to any podman or docker calls. Internally ansible-
                        builder makes use of ANSIBLE_GALAXY_CLI_COLLECTION_OPTS, ANSIBLE_RUNNER_IMAGE,
                        PYTHON_BUILDER_IMAGE.
  -v {0,1,2,3}, --verbosity {0,1,2,3}
                        Increase the output verbosity, for up to three levels of verbosity (invoked via
                        "--verbosity" or "-v" followed by an integer ranging in value from 0 to 3)
                        (default: 2)