improvement(scully): add routes validation

[Villanuevand]

When plugins generate routes for scully, we need to validate that the handledRoutes.route start with
/. In this change we show a warning.

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/scullyio/scully/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?
Add validation to Handled Routes.

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

• Yes
• No

Other information

[aaronfrost]

I like this change, here is why:

• We could have failed the build when we detect this. But since we haven't discussed it as a team, I like starting with the error and we can upgrade to a failed build if we decide that is better.
• We could have just auto-added the / to the beginning of the route, but since we haven't talked about that approach as a team, I like adding a warning for now and we can always upgrade to this later if we decide to as a team.

I am approving this, but would like to see what @SanderElias says before we merge.

[aaronfrost]

We need to add a pre-commit hook that runs prettier on all files. This reformatting done on @Villanuevand's machine should have been done by whoever wrote this code.

We need to get everyone to turn on their prettier formatting in their IDE, and we need to get a pre-commit hook that formats your stuff for prettier.

[SanderElias]

LGTM

[Villanuevand]

@aaronfrost
Issue #143 was created to solve the code format problem.