Allow choosing a default shell for terminal, failing which, fall back to sh if the default shell fails to start

[starfishpatkhoo]

⚠️ Please verify that this feature request has NOT been suggested before.

• I checked and didn't find similar feature request

🏷️ Feature Request Type

UI Feature

🔖 Feature description

Allow setting the default shell to be used when opening a shell session into a container, with a fall back to sh if the chosen shell does not exist/fails to launch.

✔️ Solution

1. Add an Environment Variable DOCKGE_DEFAULT_SHELL to specify sh, bash, zsh, tcsh .. as needed/popular
2. If DOCKGE_DEFAULT_SHELL does not exist, the default is sh
3. The Switch to shell button should list only the 4 (or 5) most popular shells
4. If people really had another shell outside of the popular ones, then they can always point to it directly via http://url:port/terminal/container/<shell> ...
5. If the shell fails to start for that container, fall back to sh instead
6. The default shell for dockge should be sh since almost every system out there has an sh (even if many people may consider it crap)

If the proposed feature request is difficult to do, then I propose (Alternate Solution):

1. Keep the default shell as bash (current behaviour)
2. If bash fails to start for that container, fall back to sh instead

❓ Alternatives

This was also brought up in - #658 - but I wrote this feature request to make it clearer.

📝 Additional Context

No response