uploads: allow searching uploads and media assets by metatag.

Allow searching the /uploads and /media_assets pages by the following metatags:

* id:
* md5:
* width:
* height:
* duration:
* mpixels:
* ratio:
* filesize:
* filetype:
* date:
* age:
* status:<processing|active|deleted|expunged|failed> (for /media_assets)
* status:<pending|processing|active|failed> (for /uploads)
* is:<filetype>, is:<status>
* exif:

Examples:

* https://betabooru.donmai.us/media_assets?search[ai_tags_match]=filetype:png
* https://betabooru.donmai.us/uploads?search[ai_tags_match]=filetype:png

Note that in /uploads search, the id:, date:, and age: metatags refer to the upload media asset, not
the upload itself.

Note also that uploads may contain multiple assets, so for example searching uploads by
`filetype:png` will return all uploads containing at least one PNG file, even if they contain other
non-PNG files.

app/models/upload.rb

@@ -126,7 +126,7 @@ class Upload < ApplicationRecord
   end
 
   def self.ai_tags_match(tag_string, score_range: (50..))
-    upload_media_assets = AITagQuery.search(tag_string, relation: UploadMediaAsset.all, foreign_key: :media_asset_id, score_range: score_range)
+    upload_media_assets = MediaAssetQuery.search(tag_string, relation: UploadMediaAsset.joins(:media_asset), foreign_key: :media_asset_id, score_range: score_range)
     where(upload_media_assets.where("upload_media_assets.upload_id = uploads.id").arel.exists)
   end