Display SVG files as images instead of text (#14101)

* Change to display SVG files as images

* Remove unsafe styles from SVG CSP

* Add integration test to test SVG headers

* Add config setting to disable SVG rendering

* Add test for img tag when loading SVG image

* Remove the Raw view button for svg files since we don't fully support this

* Fix copyright year

* Rename and move config setting

* Add setting to cheat sheet in docs

* Fix so that comment matches cheat sheet

* Add allowing styles in CSP based on pull request feedback

* Re-enable raw button since we show SVG styles now

* Change so that SVG files are editable

* Add UI to toggle between source and rendered image for SVGs

* Change to show blame button for SVG images

* Fix to update ctx data

* Add test for DetectContentType when file is longer than sniffLen

Co-authored-by: Jonathan Tran <jon@allspice.io>
Co-authored-by: Kyle D <kdumontnu@gmail.com>

docs/content/doc/advanced/config-cheat-sheet.en-us.md

@@ -194,6 +194,10 @@ Values containing `#` or `;` must be quoted using `` ` `` or `"""`.
 - `TIMEOUT_STEP`: **10s**.
 - `EVENT_SOURCE_UPDATE_TIME`: **10s**: This setting determines how often the database is queried to update notification counts. If the browser client supports `EventSource` and `SharedWorker`, a `SharedWorker` will be used in preference to polling notification endpoint. Set to **-1** to disable the `EventSource`.
 
+### UI - SVG Images (`ui.svg`)
+
+- `ENABLE_RENDER`: **true**: Whether to render SVG files as images.  If SVG rendering is disabled, SVG files are displayed as text and cannot be embedded in markdown files as images.
+
 ## Markdown (`markdown`)
 
 - `ENABLE_HARD_LINE_BREAK_IN_COMMENTS`: **true**: Render soft line breaks as hard line breaks in comments, which