Video Block: Enable inserting video from Media Library on Personal/free plans for already uploaded videos

#### Steps to reproduce the issue

1. Insert the core Video Block on a site that's on a free or Personal plan
2. A notice will say "Upgrade your plan to use this Premium Block"

#### What I expected
I expected to be able to insert videos already uploaded to the Media Library, even if the site is on a lower plan. I can think of two scenarios in which a site could have videos in its ML, despite being on a free or Personal plan:

- The videos were uploaded in the past, while the site was on a Premium or above plan
- The videos were uploaded while on a free plan, but using the mobile app (which will let you upolad videos to a simple site on a free or Personal plan).

#### What happened instead
Both the "Upload" and "Media Library" options are disabled. Interestingly enough the block will allow me to insert a video from an URL. This means that we can work around this limitation by copying the URL from the ML for an already uploaded video and pasting the it there, but this makes the block unnecessarily complicated.

We could fix this by enabling the "Media Library" button and making the message clearer (**"Upgrade your plan to _upload_ new videos"**)

**Screenshots**

Reproduce the core Video Block on a free or Personal plan and inspect the controls that gate Upload and Media Library. Trace the plan check and the block’s notice; done means existing Media Library videos can be selected, new uploads remain restricted, and the message clearly refers to uploading new videos.

Written by the indexing model from the issue text.