Is the proposal issue necessary or not?

[danthe1st]

The README mentions:

All content must start with a Content Proposal. This will be in the form of a GitHub issue using the Content Proposal issue template.

and it differentiates from requests as it seems to expect a [requested] issue before that:

Look through the requested issues and find something that you feel uniquely capable of writing

This also seems to be strengthened by the Content Proposal issue template which expects a Request Issue.

However, it seems that the [approved] label is typically put on accepted content requests (at least after this repo was opened for Community Contributions).
Furthermore, both #45 and #49 didn't seem to need a proposal issue, the request (followed by the future author being assigned to it) seemed to be sufficient.

Therefore, I propose to remove the distinction between content proposals. I would suggest to:

• Add an issue template for requests (or remove the Request Issue field from the Content Proposal template).
• Create a Pull Request template from the current Content Proposal template since it makes sense for PRs to mention the request issue (and all other fields from there).
• Clean up the tags so only the tags actually being used are listed. For example, I haven't seen any usage of the [in progress] label.
• Adapt the README to reflect this workflow.