Migrate content from rapidsai/docs to rapidsai/rapids.ai

[ajschmidt8]

As part of rapidsai/docs#388, we need to migrate all of the content from rapidsai/docs to rapidsai/rapids.ai.

For this task, we should do the following:

• Migrate all of the content
• Prune any metadata that isn't relevant to the new Hugo structure
• Ensure URLs/paths are as desired
• Ignore any style issues (these will be addressed in a separate PR)
• Remove any old Jekyll syntax that isn't valid in Hugo

[ajschmidt8]

A lot of the written content has been migrated.

However, we need to make sure we copy over all of the images as well.