Prepare docs for sub-packages

[leofang]

Close#94. Close#95.

This PR prepares for the documentation infrastructure for adding sub-packages. This introduces a (hopefully one-time only) breaking change to the existing doc urls. Two major changes are:

• cuda-python becomes a landing page for sub-packages (to prepare for RFC: Turn cuda-python into a metapackage #105)
• subdirectories are used for sub-packages' docs
• multi-version doc support is added

Old urls:

• https://nvidia.github.io/cuda-python/
  • https://nvidia.github.io/cuda-python/overview.html
  • https://nvidia.github.io/cuda-python/install.html
  • https://nvidia.github.io/cuda-python/release.html
  • ...

New urls:

• https://nvidia.github.io/cuda-python/
  • will redirects to https://nvidia.github.io/cuda-python/latest/
    • which will be a copy of https://nvidia.github.io/cuda-python/12.6.1/ as of today
  • https://nvidia.github.io/cuda-python/latest/release.html
  • ...
  • https://nvidia.github.io/cuda-python/12.6.1/release.html
  • ...
• https://nvidia.github.io/cuda-python/cuda-bindings
  • will redirects to https://nvidia.github.io/cuda-python/cuda-bindings/latest/
    • which will be a copy of https://nvidia.github.io/cuda-python/cuda-bindings/12.6.1/ as of today
  • https://nvidia.github.io/cuda-python/cuda-bindings/latest/overview.html
  • https://nvidia.github.io/cuda-python/cuda-bindings/latest/install.html
  • https://nvidia.github.io/cuda-python/cuda-bindings/latest/release.html
  • ...
  • https://nvidia.github.io/cuda-python/cuda-bindings/12.6.1/overview.html
  • https://nvidia.github.io/cuda-python/cuda-bindings/12.6.1/install.html
  • https://nvidia.github.io/cuda-python/cuda-bindings/12.6.1/release.html
  • ...
• https://nvidia.github.io/cuda-python/cuda-core
  • will redirects to https://nvidia.github.io/cuda-python/cuda-core/latest/
    • which will be a copy of https://nvidia.github.io/cuda-python/cuda-core/0.1.0/ as of today
  • https://nvidia.github.io/cuda-python/cuda-core/latest/install.html
  • https://nvidia.github.io/cuda-python/cuda-core/latest/release.html
  • ...
  • https://nvidia.github.io/cuda-python/cuda-core/0.1.0/install.html
  • https://nvidia.github.io/cuda-python/cuda-core/0.1.0/release.html
  • ...

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[leofang]

This should be ready for review. However, do not merge yet, as I need to do a live demo first before we commit to the changes.

[leofang]

(Updated the PR description to compare the old/existing urls with the new/expected urls.)

[vzhurba01]

LGTM