Add shellcheck shell script files linter

[MareStare]

Before you begin

• I understand my contributions may be rejected for any reason
• I understand my contributions are for the benefit of Derpibooru and/or the Philomena software
• I understand my contributions are licensed under the GNU AGPLv3

• I understand all of the above

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See the tool repo for details. Yeah it's written in Haskell

[MareStare]

Note that we are now pinning the version of typos, when previously we were using the master version of typos on CI. I think pinning the tool version is actually better in general, especially in case of typos because typos can produce new lints between patch releases. So every time typos does a release it breaks Philomena's CI.

Instead, we should bump the version of typos explicitly.

[Meow]

I... think this is going a tad too far with all the linting, considering you're adding this huge thing and this whole additional step, for the sake of files which we almost never modify.

[MareStare]

I can remove it from the precommit hook if its perf is concerning you, but I expect to extend the dev scripts over time. I don't think this linter costs anything. I specifically made it so that adding new linters is extremely easy in this PR by splitting the existing init.sh script into several files per each tool, otherwise the changes in this PR would be much smaller

[MareStare]

Superseded by #528