CLI Workflow[Template] documentation generator

[elliotgunton]

Is your feature request related to a problem? Please describe.
Originally described in #670. Would be good to get consistent docs for Workflow[Templates].

Describe the solution you'd like
hera generate docs FROM [--to <filepath>] [-o yaml|json|markdown]

Which would output the input/output interface of the templates in the Workflow[Template], as well as any doc strings in labels/annotations. e.g. in markdown form, it might look something like:

# Hello World Workflow

This is a test workflow

entrypoint: [Hello World](#hello world)

## Hello World

This prints "Hello <name>" to stdout.

### Inputs

Param | Type | Default
--- | --- | ---
name | str | "World"

which renders as:

Hello World Workflow

This is a test workflow

entrypoint: [Hello World](#hello world)

Hello World

This prints "Hello " to stdout.

Inputs

Param	Type	Default
name	str	"World"

from a workflow like:

@script(
    constructor="runner",
    image="something:v1",
    annotations={"com.hera.docstring": 'This prints "Hello <name>" to stdout.'},
)
def hello(name: str):
    print("Hello, {name}!".format(name=name))


with Workflow(
    generate_name="hello-world-",
    entrypoint="hello",
    arguments={"s": "world"},
    annotations={
        "com.hera.docstring": "This is a test workflow",
    },
) as w:
    hello()

Unsure about json/yaml format but probably useful for devs to create their own docs.

Describe alternatives you've considered
Write your own custom thing.

Additional context
Add any other context or screenshots about the feature request here.