Breaking: `report-message-format` should apply to suggestion messages

[bmish]

The report-message-format only applies to violation messages, but not suggestion messages.

As a breaking change, we should update it to apply to both violation and suggestion messages.

report-message-format: ['error', '^[A-Z].*\\.$']

As a follow-up (non-breaking change), we could add object-based options to the rule to allow separate violation/suggestion message requirements:

report-message-format: ['error', { error: '^[A-Z].*\\.$', suggestion: '^[A-Z].*\\.$' }]