Enhance extension and config docs

[MarcSkovMadsen]

Closes #3404

You can preview the docs here

I've used the script below to generate the options summary section.

import panel as pn
from textwrap import dedent
import textwrap

NO_ENVIRONMENT_VARIABLE=[
    '_admin', '_theme'
]

ENVIRONMENT_VARIABLE_NAME={
    "_oauth_encryption_key": "PANEL_OAUTH_ENCRYPTION",
    "_nthreads": "PANEL_NTHREADS",
}

def nice_name(key):
    if key.startswith("_"):
        return key[1:]
    return key

def environment_variable(key):
    if key in NO_ENVIRONMENT_VARIABLE:
        return ""
    if key in ENVIRONMENT_VARIABLE_NAME:
        return f" (`{ENVIRONMENT_VARIABLE_NAME[key]}`)" 
    if key.startswith("_"):
        return f" (`PANEL{key.upper()}`)"
    return ""

def nice_default_value(parameter):
    default=parameter.default
    if isinstance(default, str):
        return f"'{default}'"
    return str(default)

def nice_type(parameter):
    if parameter.__class__.__name__ in ["Selector", "ObjectSelector"]:
        return f"""Literal | Options: '{"', '".join([str(object) for object in parameter.objects])}'"""
    return parameter.__class__.__name__

def is_readonly(parameter):
    original = parameter.name.startswith("_") or parameter.constant or parameter.readonly
    new = False
    try:
         setattr(pn.config, parameter.name, getattr(pn.config, parameter.name))
    except:
        new = True
    return new

keys_and_parameters = [(key, pn.config.param[key]) for key in pn.config.param.values() if key!="name"]
keys_and_parameters = sorted(keys_and_parameters, key=lambda x: nice_name(x[0]))

def print_parameters(parameters):
    for key, parameter in parameters:    
        text = f"""\
### `{nice_name(key)}`{environment_variable(key)}

{dedent(pn.config.param[key].doc)}

Default: {nice_default_value(parameter)} | Type: {nice_type(parameter)}
"""
        text = text.replace("`\n\n", "`\n").replace("`)\n\n\n", "`)\n\n")
        print(text)

print("## Options Summary\n")

print_parameters(keys_and_parameters)

[codecov]

Codecov Report

Merging #5790 (f3e43eb) into main (359ccbe) will increase coverage by 9.94%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##             main    #5790      +/-   ##
==========================================
+ Coverage   72.44%   82.39%   +9.94%     
==========================================
  Files         290      290              
  Lines       42161    42164       +3     
==========================================
+ Hits        30544    34740    +4196     
+ Misses      11617     7424    -4193     

Flag	Coverage Δ
ui-tests	38.31% <75.00%> (?)
unitexamples-tests	72.44% <75.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
panel/config.py	66.98% <75.00%> (-0.01%)	⬇️

... and 70 files with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[philippjfr]

Looks good, thanks!