chore(template): separate issue url from body (#27216)

Now that the default commit message uses the PR description, the
conventional commit tool is getting confused when it sees other URLs and
text that looks like issues (like hex colors).

Using the `-------` separates the issue URL from the rest of the PR
description and helps the conventional commits tool generate the
changelog correctly.

Example:
https://github.com/ionic-team/ionic-framework/releases/tag/v7.0.3-nightly.20230417

`item: ios active state has correct contrast` has issue 000 as the issue
the commit closes. This is happening because I mentioned the 000 hex
color in the commit description.