Linter to warn if the summary field is over 78 characters

[lengau]

What needs to get done

If the summary field is more than 78 characters long, warn the user during the linting process.

Why it needs to get done

Charmcraft 3.0 introduces a summary length limit, but 78 broke too many charms. At a future point, we can revisit this limit and reduce it.

[syncronize-issues-to-jira]

Thank you for reporting us your feedback!

The internal ticket has been created: https://warthogs.atlassian.net/browse/CRAFT-2599.

This message was autogenerated