Fail docs build when there are broken links

[mfisher87]

Depends on #534

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📚 Documentation preview 📚: https://earthaccess--535.org.readthedocs.build/en/535/

[mfisher87]

INFO    -  Cleaning site directory
INFO    -  Building documentation to directory: /home/docs/checkouts/readthedocs.org/user_builds/earthaccess/checkouts/535/_readthedocs/html
INFO    -  The following pages exist in the docs directory, but are not included in the "nav" configuration:
  - contributing/development.md
  - contributing/releasing.md
  - howto/access-data.md
  - tutorials/getting-started.ipynb
WARNING -  Doc file 'quick-start.md' contains a relative link 'user_guide.qmd', but the target is not found among documentation files.
WARNING -  Doc file 'quick-start.md' contains a relative link 'how_to.qmd', but the target is not found among documentation files.
WARNING -  Doc file 'quick-start.md' contains a relative link 'authenticate.qmd', but the target is not found among documentation files.
INFO    -  Doc file 'contributing/index.md' contains an absolute link '/CODE_OF_CONDUCT.md', it was left as is.
INFO    -  Converting notebook (execute=True): /home/docs/checkouts/readthedocs.org/user_builds/earthaccess/checkouts/535/docs/howto/edl.ipynb
INFO    -  Converting notebook (execute=True): /home/docs/checkouts/readthedocs.org/user_builds/earthaccess/checkouts/535/docs/tutorials/SSL.ipynb
INFO    -  Converting notebook (execute=True): /home/docs/checkouts/readthedocs.org/user_builds/earthaccess/checkouts/535/docs/tutorials/emit-earthaccess.ipynb
INFO    -  Converting notebook (execute=True): /home/docs/checkouts/readthedocs.org/user_builds/earthaccess/checkouts/535/docs/tutorials/file-access.ipynb
INFO    -  Converting notebook (execute=True): /home/docs/checkouts/readthedocs.org/user_builds/earthaccess/checkouts/535/docs/tutorials/getting-started.ipynb
INFO    -  Converting notebook (execute=True): /home/docs/checkouts/readthedocs.org/user_builds/earthaccess/checkouts/535/docs/tutorials/restricted-datasets.ipynb
WARNING -  Doc file 'user_guide/overview.md' contains a relative link 'user_guide/authentication.md', but the target 'user_guide/user_guide/authentication.md' is not found among documentation files.
WARNING -  Doc file 'user_guide/overview.md' contains a relative link 'user_guide/search.md', but the target 'user_guide/user_guide/search.md' is not found among documentation files.
WARNING -  Doc file 'user_guide/overview.md' contains a relative link 'user_guide/access.md', but the target 'user_guide/user_guide/access.md' is not found among documentation files.

Aborted with 6 warnings in strict mode!