feat: add make fmt for *.sh *.bash

1. add .editorconfig file, add rules for .sh .bash files.
2. add make fmt target, use:
    - gofmt *.go.
    - shfmt *.sh *.bash, shell/completion.bash, shell/key-bindings.bash
        need a left indent due to an outermost if block.
3. add shfmt check for bash scripts in make lint target.
4. install shfmt in actions.

.github/workflows/linux.yml

@@ -33,7 +33,7 @@ jobs:
         ruby-version: 3.4.1
 
     - name: Install packages
-      run: sudo apt-get install --yes zsh fish tmux
+      run: sudo apt-get install --yes zsh fish tmux shfmt
 
     - name: Install Ruby gems
       run: bundle install