Add a multi-page flags reference

### Page link:

https://bazel.build/reference/command-line-reference

### Problem description (include actual vs expected text, if applicable):

Currently the command-line-reference page has flags for every bazel subcommand. This makes using cmd+f a bit annoying since you can find flags that may not be applicable for the subcommand you're interested in, and there's no way to filter that out. I think having this page with all of them is fine, but I think there should also be a per-subcommand page to make this more scoped and easier to search through

### Where do you see this issue? (include link to specific section of the page, if applicable)

_No response_

### Any other information you'd like to share?

_No response_

Start by reviewing the existing command-line-reference page at https://bazel.build/reference/command-line-reference and how it organizes flags for each Bazel subcommand. Done means retaining the all-flags reference while adding separate, searchable reference pages scoped to individual subcommands.

Written by the indexing model from the issue text.