Set WAYBAR_OUTPUT_NAME env variable in custom module event handlers.

[rafal11ck]

WAYBAR_OUTPUT_NAME is set for exec, but not for on-click, on-scroll-up, on-scroll-down.

This can be observed with following module that dumps env to file from exec and events then compares it, diff is shown in the stdout so diff can be noticed easily when waybar is run from cli:

  "custom/events": {
    "format": "eventTest",
    "exec": "env > /tmp/debug.log ; printf 'aaa\ntip\nclass\n100\n'",
    "on-click": "env > /tmp/debug2.log && diff /tmp/debug.log /tmp/debug2.log ",
    "on-scroll-up": "env > /tmp/debug2.log && diff /tmp/debug.log /tmp/debug2.log ",
    "on-scroll-down": "env > /tmp/debug2.log && diff /tmp/debug.log /tmp/debug2.log "
  }

part of output that I get:

 34d33
< WAYBAR_OUTPUT_NAME=DP-2

This seems to be related:
#2821 (comment)