fix(hooks): make the output more uniform and delineated

[joshtrichards]

Previously:

• Some essentially similar hook folder states would result in different output (e.g. nonexistent versus empty folders)
• The completion of a given stage wasn't 100% delineated

With this PR, the broader hook handling output is more neutral/consistent while retaining detailed hints where appropriate about the state of things along the way.

Specifically:

• Always indicate when we're searching for scripts for a given stage
• Skip early if a given stage's folder is empty too
• Always indicate when we're skipping (executing nothing for) a given stage + why
• Always delineate when we've completely finished executing all found scripts for given stage
• Add the term we use for this feature in our docs to the output ("hook")
• Minor language tweaks

Tested with:

• Empty hook folders
• Nonexistent hook folders
• Scripts lacking exec permission in hook folder
• Non-*.sh files in hook folders
• Valid executable scripts in hook folder

[joshtrichards]

Cc: @dvaerum, @d0niek FYI: Just some (minor) hook related tidying

[dvaerum]

Generally it looks fine to me, but you will probably be told to fix your git history because your 2nd commit makes corrects things in your 1st commit.

I would, for readability, make the 1 commit (the 1st) focus on the logic and have a 2nd commit which fixed the echo messages there you want them improved.