Itzg Docker - correct way to set resource pack from bind-mounted folder

Hi!

Interested in hosting server with a custom map and RP combo using a docker-compose file for itzg's image. This is my config

services:
  mc:
    image: itzg/minecraft-server:latest
    tty: true
    stdin_open: true
    ports:
      - "25565:25565"

    environment:
      EULA: "TRUE"
      VERSION: "1.21.5"  # 1.21.5 needed for map
      USE_AIKAR_FLAGS: "true"
      USE_MEOWICE_FLAGS: "true"
      ENABLE_COMMAND_BLOCK: "true"

      # resourcepack and world config
      WORLD: /extras/worlds/100WaysToDie.zip
      RESOURCE_PACK: /extras/resourcepacks/100WaysToDieRP.zip

      # Fabulously optimized - used by clients too
      MODPACK_PLATFORM: "AUTO_CURSEFORGE"
      CF_PAGE_URL: https://www.curseforge.com/minecraft/modpacks/fabulously-optimized/files/6972535  # for 1.21.5
      CF_API_KEY: "******************************************"

      # server config and restrictions
      MOTD: "*************************"
      OPS: |-
        ******
      ENABLE_WHITELIST: "true"
      WHITELIST: |-
        *************
    volumes:
      - "./data:/data"
      - "./extras:/extras"

The world gets copied from the bind mounted extras folder, but the resource pack does not. From the documentation, I'm suspecting RESOURCE_PACK is only intended for URLs.

- Am I doing something obviously wrong?
- If it is indeed supposed to only be a URL, how can I manually set a locall resource pack? (eg. override config or something?)