Add a step to CI to check files have been formatted with shfmt

[triarius]

To reduce loss of productivity due to debates about the formatting of shell scripts, I've added a formatting check to the CI that uses shfmt to detect script that are not formatted in accordance with it. This complements the existing checking of lints using shellcheck.

The options I've supplied to shfmt are:

• --indent 2 to use 2 spaces for indentation. This matches our conventions for languages other than go.
• --binary-next-line which allows binary operators onto the next line

# good
echo hello world \
  | grep hello
echo hello world | grep hello

# bad
echo hello world |
  grep hello

If we didn't specify this, the first good example will be formatted to be like the first bad example, which I consider to be less readable as it requires reading to the end of the first line to see what the binary operator is, and is confusing as it does not use a line continuation at all.

[triarius]

This is a bit unfortunate, I would prefer if the formatter did not do this, but I don't consider it important enough to be fatal to the goal of having a formatter.

Luckily, to mitigate potential confusion between the end of the conditional and start of the body of the if statement, most text editors will highlight the then with coloured crayon technology.

[DrJosh9000]

🥬

[moskyb]

🥳