docs(network): Added a note about APN parameter in cellular doc

[pierantoniomerlino]

This PR adds a note about the optional APN parameter in the Cellural documentation page. See #5350 for more details.

[mattdibi]

Another note: we should also point out that it will be optional for generic profiles only. I would put that in the 5.6 version of the documentation to avoid confusion in the 6.0 docs but I'm not sure it's the easiest way 🤔

[github-actions[bot]]

The backport to docs-release-5.6 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-docs-release-5.6 docs-release-5.6
# Navigate to the new working tree
cd .worktrees/backport-docs-release-5.6
# Create a new branch
git switch --create backport-5352-to-docs-release-5.6
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 8ee10e2b8cc66bcc6b730246f2c9091429f8dce0
# Push it to GitHub
git push --set-upstream origin backport-5352-to-docs-release-5.6
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-docs-release-5.6

Then, create a pull request where the base branch is docs-release-5.6 and the compare/head branch is backport-5352-to-docs-release-5.6.