Operating system specific versions of shell commands + shell selection

[Taitava]

Discussed in https://github.com/Taitava/obsidian-shellcommands/discussions/38

Write possible comments to the above mentioned discussion. This task is just for Roadmap planning, branching, and time logging.

[Taitava]

A possible backwards incompatible change

SC versions prior to 0.7.0 used /bin/sh as a shell on Linux and Mac (/bin/sh came as a default value from Node.js's child_process).

• Linux & Mac: 0.7.0 changes this so that the default shell is retrieved from the current user's $SHELL environment variable. The reason for this change is that I think it's more logical to use a default shell that is defined in the operating system's user's preferences, rather than a hardcoded default shell defined by Node.js, as not many users even know that it comes from Node.js, and not many users know what Node.js is.
• On Windows, default shell is retrieved from COMSPEC environment variable, and this has not changed.
• These are only defaults, and a user can change these shells in settings.

If a shell has changed for you, your shell commands might run a bit differently after this upgrade.

[Taitava]

This feature should also be pretty well baked at the moment. Let's see how it performs in the beta test.

[Taitava]

Done & released.