feat: specify current spatial browser supported file types in the media gallery modal

[tnrdd]

Description

Update the text in the gallery modal to specify the file types currently supported by the Geo Web Spatial Browser. Only allow uploads of .glb and .usdz files but allow already uploaded media objects to be edited even if their content is not a 3D model.

Issue

fixes #365

Checklist:

• [x] My commit message follows the Conventional Commits specification
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have tested my code
• [x] My changes generate no new warnings
• [x] My PR is rebased off the most recent develop branch
• [x] My PR is opened against the develop branch

Alert Reviewers

@codynhat @gravenp