Feature request: Allow to go back to auto-detect encoding

**Is your feature request related to a problem? Please describe.**
By default, cyberchef does auto-detect of the encoding. But once you set a specific encoding in the out pane, you cannot go back to "auto-detect" mode. Or at least I haven't found a way using UI.

Steps to reproduce:
1. Generate some output
2. In the output pane select a specific encoding (eg: UTF-8)
3. Change the output so the content is on a different encoding.

The output will not auto-detect the encoding anymore.

**Describe the solution you'd like**
There should be an option called "auto-detect" in the encodings drop down, to allow to go back to that mode.

**Describe alternatives you've considered**
The workaround is to bake the recipe, stripe the "oenc" from the URL and load again.

**Additional context**
Probably the same happens to line detection mode.

Start at the output pane's encoding drop-down and trace how the selected encoding, including the oenc URL setting, is stored and restored. Done means the drop-down offers an auto-detect option that restores automatic encoding detection after a specific encoding was selected; line detection is mentioned as possible related work but is not defined.

Written by the indexing model from the issue text.