Force hooks to specify their target version

## Problem
Currently, hooks have the possibility to validate that the current hook version matches
their target (e.g., something like: `[ "$1" = "api:2" ] || { echo "Invalid version: $1"; exit 1; }`).

But this is completely voluntary, and not inspectable from the outside. Thus, TW has no
way to know which version a certain hook is targeting, and if it should warn the user
about outdated hooks.

## Proposed improvement
If we moved the hook naming scheme from `` to
`-`, we would require hooks to specify what version they are
targeting.

The changes from a v2 hook directory to a v3:

### V2
```
$ tree ~/.config/task/hooks
/nix/store/qicdpkw69wzp8gxi52i73h4ddaqy5k14-mk-taskwarrior-hooks
├── on-add_enforce-projects
├── on-add_sync-git-repos
├── on-modify_sync-git-repos-mod
├── on-modify_track-timewarrior
└── on-modify_track-total-active-time

1 directory, 5 files
```

### V3
```
$ tree ~/.config/task/hooks
/nix/store/qicdpkw69wzp8gxi52i73h4ddaqy5k14-mk-taskwarrior-hooks
├── on-add-v3_enforce-projects
├── on-add-v3_sync-git-repos
├── on-modify-v3_sync-git-repos-mod
├── on-modify-v3_track-timewarrior
└── on-modify-v3_track-total-active-time

1 directory, 5 files
```

This could also be used to have a hook API version per type, but that seems to be
irrelevant for now.