☂️ Auto-indexing docs enhancements

[varungandhi-src]

• https://docs.sourcegraph.com/code_navigation/references/inference_configuration is not linked from https://docs.sourcegraph.com/code_navigation
• https://docs.sourcegraph.com/code_navigation/references/auto_indexing_configuration and https://docs.sourcegraph.com/code_navigation/references/inference_configuration have very similar titles
• Document pre-requisites for auto-indexing
• https://github.com/sourcegraph/sourcegraph/issues/56528
• Add better docs on the preferred workflow for C#/VB. We got a question in Slack related to this; right now, we don't have a clear recommendation in the docs on the most preferred option.
• https://github.com/sourcegraph/sourcegraph/issues/57694
• Document environment variables for auto-inference #61281