Create action to check valid commit subjects

[josecelano]

@da2ce7 proposed to create a workflow that forbids other commits to start with the same prefix as the queue.

We use the first Character to Identify the Queue Commits. Maybe we should then remove the "📝" character. Then we should have a workflow that forbids any other commit to start with the "🈺", "⬆️" and "⬇️" emojis.

Originally posted by @da2ce7 in #21 (comment)

• Create an action that validates the commit subject. It should make the workflow fail when there is a commit with one of these emojis: "🈺", "⬆️" and "⬇️".
• Add the workflow to the sample projects: library-consumer, chinese-ideaographs-website.

NOTES:

• We have to check if the first character is a queue prefix but we also have to check that is not a legitimate queue subject. Maybe we can check if the first character is the emoji but the second is not the queue delimiter.
• We should check all the new commits that are going to be added to the target branch.

@da2ce7 was that your idea?