docs(cells): update rake command for ids

What does this merge request do and why?

What

Update the rake command to use bundle exec rake

Why

When using rake directly you end up using the global rake gem you have installed, bundle exec rake will use the correct version.

Using the global version can result in the follow errors:

$ rake gitlab:db:cells:bump_cell_sequences\[10000\]
rake aborted!
Gem::LoadError: You have already activated rake 13.1.0, but your Gemfile requires rake 13.0.6. Prepending `bundle exec` to your command may solve this.

How to set up and validate locally

Follow the docs instruction that the merge request is updating

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Merge request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise an issue to follow-up.
• Documentation added/updated, if needed.
• Announcement added, if change is notable.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.