separate node and python build steps in dash-generate-components

[python273]

Links for building custom components for reference:
https://dash.plotly.com/plugins
https://github.com/plotly/dash-component-boilerplate

Is your feature request related to a problem? Please describe.
Building custom dash components requires nodejs + python at the same time. It complicates CI pipeline, since it's not possible to use docker's node and python images separately, but you have to make a custom docker image with both

my Dockerfile for reference

FROM ubuntu:latest

ENV DEBIAN_FRONTEND=noninteractive

RUN apt-get update && \
    apt-get install nodejs npm python3 python3-pip -y && \
    node --version && \
    python3 --version && \
    python3 -m pip install "dash[dev]>=1.3.1"

COPY ./custom_dash_components/package.json /src/custom_dash_components/
COPY ./custom_dash_components/package-lock.json /src/custom_dash_components/
WORKDIR /src/custom_dash_components/
RUN npm i

COPY ./custom_dash_components/ /src/custom_dash_components/

RUN npm run build:js && npm run build:py

build:py is dash-generate-components ./src/lib/components custom_dash_components -p package-info.json

Describe the solution you'd like

I think it's possible to separate nodejs and python build steps, so

1. nodejs step would build js code and generate metadata file
2. python step would take metadata file as a cmd arg and generate python code

Related code

dash/dash/development/component_generator.py

Lines 55 to 90 in 066e571

	extract_path = pkg_resources.resource_filename("dash", "extract-meta.js")
	reserved_patterns = "|".join("^{}$".format(p) for p in reserved_words)
	os.environ["NODE_PATH"] = "node_modules"
	cmd = shlex.split(
	'node {} "{}" "{}" {}'.format(
	extract_path, ignore, reserved_patterns, components_source
	),
	posix=not is_windows,
	)
	shutil.copyfile(
	"package.json", os.path.join(project_shortname, package_info_filename)
	)
	proc = subprocess.Popen(
	cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=is_windows
	)
	out, err = proc.communicate()
	status = proc.poll()
	if err:
	print(err.decode(), file=sys.stderr)
	if not out:
	print(
	"Error generating metadata in {} (status={})".format(
	project_shortname, status
	),
	file=sys.stderr,
	)
	sys.exit(1)
	metadata = safe_json_loads(out.decode("utf-8"))

Describe alternatives you've considered
Another option is to generate python code in nodejs, so python is not required, but I'd guess that's harder to implement