🌐 Fix live docs server for translations for some languages

[wakabame]

Docs for tests fail in some languages due to undefined 'sponsors' (fr, ja, zh) or no docs/ in dir(az):

`python ./scripts/docs.py live ja`

$ python ./scripts/docs.py live ja
ERROR:mkdocs.commands.build:Error reading page 'fastapi-people.md': 'sponsors' is undefined
Traceback (most recent call last):
  File "./scripts/docs.py", line 449, in <module>
    app()
  File "/home/wakabame/fastapi/env/lib/python3.8/site-packages/typer/main.py", line 214, in __call__
    return get_command(self)(*args, **kwargs)
  File "/home/wakabame/fastapi/env/lib/python3.8/site-packages/click/core.py", line 829, in __call__
    return self.main(*args, **kwargs)
  File "/home/wakabame/fastapi/env/lib/python3.8/site-packages/click/core.py", line 782, in main
    rv = self.invoke(ctx)
  File "/home/wakabame/fastapi/env/lib/python3.8/site-packages/click/core.py", line 1259, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/wakabame/fastapi/env/lib/python3.8/site-packages/click/core.py", line 1066, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/wakabame/fastapi/env/lib/python3.8/site-packages/click/core.py", line 610, in invoke
    return callback(*args, **kwargs)
  File "/home/wakabame/fastapi/env/lib/python3.8/site-packages/typer/main.py", line 497, in wrapper
    return callback(**use_params)  # type: ignore
  File "./scripts/docs.py", line 357, in live
    mkdocs.commands.serve.serve(dev_addr="127.0.0.1:8008")
  File "/home/wakabame/fastapi/env/lib/python3.8/site-packages/mkdocs/commands/serve.py", line 54, in serve
    config = builder()
  File "/home/wakabame/fastapi/env/lib/python3.8/site-packages/mkdocs/commands/serve.py", line 49, in builder
    build(config, live_server=live_server, dirty=dirty)
  File "/home/wakabame/fastapi/env/lib/python3.8/site-packages/mkdocs/commands/build.py", line 292, in build
    _populate_page(file.page, config, files, dirty)
  File "/home/wakabame/fastapi/env/lib/python3.8/site-packages/mkdocs/commands/build.py", line 170, in _populate_page
    page.markdown = config['plugins'].run_event(
  File "/home/wakabame/fastapi/env/lib/python3.8/site-packages/mkdocs/plugins.py", line 102, in run_event
    result = method(item, **kwargs)
  File "/home/wakabame/fastapi/env/lib/python3.8/site-packages/markdownextradata/plugin.py", line 99, in on_page_markdown
    return self.apply_template(markdown)
  File "/home/wakabame/fastapi/env/lib/python3.8/site-packages/markdownextradata/plugin.py", line 111, in apply_template
    return md_template.render({**self.mkdocsConfig, **self.mkdocsConfig.get("extra")})
  File "/home/wakabame/fastapi/env/lib/python3.8/site-packages/jinja2/environment.py", line 1291, in render
    self.environment.handle_exception()
  File "/home/wakabame/fastapi/env/lib/python3.8/site-packages/jinja2/environment.py", line 925, in handle_exception
    raise rewrite_traceback_stack(source=source)
  File "<template>", line 118, in top-level template code
  File "/home/wakabame/fastapi/env/lib/python3.8/site-packages/jinja2/environment.py", line 474, in getattr
    return getattr(obj, attribute)
jinja2.exceptions.UndefinedError: 'sponsors' is undefined

`python ./scripts/docs.py live az`

$ python ./scripts/docs.py live az
ERROR:mkdocs.config:Config value: 'docs_dir'. Error: The path /home/wakabame/fastapi/docs/az/docs isn't an existing directory.
Aborted with 1 Configuration Errors!

• Since the sponsor is not defined in the development environment, we need check {% if sponsors %} before {% if sponsors.gold %}.
• In docs/az/docs, temporarily create .gitkeep to make the directory aware

[codecov]

Codecov Report

Merging #4729 (e24d50f) into master (0d1be46) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master     #4729   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          531       531           
  Lines        13629     13629           
=========================================
  Hits         13629     13629           

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[github-actions]

📝 Docs preview for commit 53bd7a9 at: https://62692b82115c23170382e0c6--fastapi.netlify.app

[tiangolo]

Good catch, thank you @wakabame ! 🚀

[wakabame]

@tiangolo
Thank you for your review and acceptance!