load_external_modules works not as a global-only option

[monosans]

Describe the bug
Docs state that load_external_modules is a global-only option:

plugins:
  - mkdocstrings:
      handlers:
        python:
          load_external_modules: true

In fact, it makes effect only when used inside options key:

plugins:
  - mkdocstrings:
      handlers:
        python:
          options:
            load_external_modules: true

System (please complete the following information):

• mkdocstrings-python version: 1.2.0
• Python version: 3.11.3
• OS: Arch Linux

[pawamoy]

Thanks for the report, and good catch! Will fix asap