feat: configure mime/type option

[Pintorado]

Description

This PR improves audio file handling in the Mux plugin and adds configurable MIME type validation. It builds upon the work from PR #398 by @isaac-martin.

Closes issue #382, which calls for better audio file handling and support in the plugin, and it also closes #407 by fixing the state of the input on dragEnter for audios.

What to review

• Added acceptedMimeTypes configuration option that allows configuring which file types are accepted by the input ('video/*' and/or 'audio/*'). Default value is ['video/*', 'audio/*']
• Fixed audio preview after upload: audio files now display correctly in the player component after being uploaded. Also added an image that reflects the audio type of the file.
• Updated terminology from "video" to "asset" across multiple components to reflect support for both video and audio files.
• Updated README.md with comprehensive documentation for the acceptedMimeTypes configuration option.

Testing

There are 2 options to configure the acceptedMimeTypes:

1) Plugin-level configuration

Configure accepted file types for all mux.video fields globally:

import {muxInput} from 'sanity-plugin-mux-input'

export default defineConfig({
  plugins: [
    muxInput({
      acceptedMimeTypes: ['video/*'], // Only accept video files
      // or
      acceptedMimeTypes: ['audio/*'], // Only accept audio files
      // or
      acceptedMimeTypes: ['video/*', 'audio/*'], // Accept both (default)
    }),
  ],
})

2) Schema-level configuration

Configure accepted file types for individual fields in your schema, which will override the plugin-level configuration:

import { defineField, defineType } from "sanity";

export default defineType({
  name: "muxTest",
  title: "Mux Files",
  type: "document",
  fields: [
    defineField({
      name: "audioFile",
      title: "Audio File",
      type: "mux.video",
      options: {
        acceptedMimeTypes: ["audio/*"],
      },
    }),
    defineField({
      name: "videoFile",
      title: "Video File",
      type: "mux.video",
      options: {
        acceptedMimeTypes: ["video/*"],
      },
    }),
    defineField({
      name: "either",
      title: "Either File",
      type: "mux.video",
    }),
  ],
});

Try uploading audios, videos and other unsupported file types in the different uploaders. Verify that each uploader accepts only the file types specified in its acceptedMimeTypes configuration (by default, accepts both audio and video files). After uploading an audio, check that the preview displays correctly.

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[R-Delfino95]

LGTM!
@stipsan, this should be ready for review and merge 😄

[stipsan]

Thank you! 💖