Move "Contributing to Openverse" docs section to "General development guidelines" header

[AetherUnbound]

Problem

Presently, we have two primary sections of information that are useful for new contributors and exist in two entirely separate locations within the docs hierarchy:

1. General development guidelines (/general)
2. Contributing to Openverse (/meta/contribution)

Description

We should move the latter (/meta/contribution) documents under /general so they are co-located with documentation that's useful for new contributors. Trying to find the "Contributing to Openverse" documentation might be difficult for new contributors who are poking around our documentation tree - I have seen firsthand that their instinct is to go towards "General development guidelines" rather than "Managing the Openverse" (since they're not actually looking to do the latter).

Note: We will want to ensure that we have redirects for the old pages set up.

Since the pages are both important and frequently referenced, we will want to set up redirects from the old page locations to the new ones. Examples of previous redirects can be found here:

https://github.com/WordPress/openverse/blob/b2f3fd6a38b473d00b50db61a83f625e05042a6c/documentation/conf.py#L92-L100

We can use a wildcard to redirect the entire folder: https://documatt.com/sphinx-reredirects/usage.html#redirect-existing-documents

As such, I believe the change would be moving /meta/contribution/ to /general/contribution/, and then adding a redirect like so:

redirects = {
    "meta/contribution/*": "/general/contribution/${source}.html"
}

Additional context