Make clj-depend more extensible through hooks

[fabiodomingues]

clj-depend was created to be a Clojure namespace dependency analyzer. For the project's objective to remain true, it is necessary to make it more extensible, so that people can build their own checks using clj-depend itself instead of building parallel tools or building linters using other tools (that do not have the exclusive objective of being a namespace analyzer as clj-depend).

A good reference is how hooks work in clj-kondo: https://github.com/clj-kondo/clj-kondo/blob/master/doc/hooks.md