So, If for anyone who got the same problem as me, here how I got to work:

I have written the following commands to a bin/setup (autogenerated file by Rails).

puts "Installing zsh, plugins and its theme..."

# Executar comandos bash dentro do Ruby
system <<-BASH
  sh -c "$(wget -O- https://github.com/deluan/zsh-in-docker/releases/download/v1.2.1/zsh-in-docker.sh)" -- \
      -p git \
      -p https://github.com/zsh-users/zsh-autosuggestions \
      -p https://github.com/zsh-users/zsh-syntax-highlighting \
      -a 'export TERM=xterm-256color'

  echo 'DISABLE_AUTO_UPDATE=true' >> ~/.zshrc
  echo 'DISABLE_UPDATE_PROMPT=true' >> ~/.zshrc
  echo '[[ ! -f ~/.p10k.zsh ]] || source ~/.p10k.zsh' >> ~/.zshrc
  echo 'eval "$(rbenv init -)"' >> ~/.zshrc
BASH

puts "Zsh configuration complete!"

This file is executed through the "postCreateCommand": "bin/setup --skip-server" at the end of the devcontainer.json file. Also I have my .zsh_history and .pd10k at a folder .docker/zsh inside my project to keep the history and the pd10k configuration and the following code inside my compose.yaml:

volumes:
      - ..:/workspaces/project-name:cached
      - ../.docker/zsh/powerlevel10k/.p10k.zsh:/home/vscode/.p10k.zsh:delegated
      - ../.docker/zsh/history/.zsh_history:/home/vscode/.zsh_history:delegated

Its both at .gitignore so each person has its own powerlevel10k configuration and zsh history. That it is!

Things that I also tried:

To use the zsh-plugins devcontainer plugin as follows:

"ghcr.io/devcontainers-extra/features/zsh-plugins:0": {
  plugins: "zsh-autosuggestions zsh-syntax-highlighting",
  omzPlugins: "ttps://github.com/zsh-users/zsh-autosuggestions.git https://github.com/zsh-users/zsh-syntax-highlighting.git"
}

And it also worked great! I would just place as last feature just to be sure.

What it didn't work:

• To use the devcontainer feature powerlevel10k. It looks like the feature wasn't even there.
• To use the devcontainer feature zsh and define its theme as "powerlevel10k/powerlevel10k" and plugins as "zsh-autosuggestions zsh-syntax-highlighting". The plugins weren't installed and neither the powerlevel10k theme. But at least it updated the ~/.zshrc file.