feat: add workflow for checking unresolved conflicts

[asdolo]

What does this do?

This PR adds a new GitHub workflow that checks if there are unresolved conflicts in the code and it fails if they are.

Why did you do this?

• To add an extra safety check in our pipeline.
• It is part of a bigger task that involves automating the update process of a project that was created using this template. That automation script tries to solve merge conflicts as best as possible, but in some cases it introduces some merge conflicts that GitHub's interface doesn't show as Merge Conflict in the Pull Request page.

Who/what does this impact?

Every project using the next version of the template. They should add the new "check-conflicts" check in their branch protection ruleset: (Repository settings > Rules > Rulesets > Select branch protection ruleset > Expand "Require status checks to pass" rule > Click on "Add checks" and select the "check-conflicts" check).

How did you test this?

I tested the workflow in a temporal test repository.

[github-actions]

💯 Test Coverage

Lines	Statements	Branches	Functions
	50.69% (256/505)	46.63% (104/223)	36.12% (69/191)

😎 Tests Results

Tests	Skipped	Failures	Errors	Time
68	0 💤	0 ❌	0 🔥	26.683s ⏱️

👀 Tests Details • (51%)

File	% Stmts	% Branch	% Funcs	% Lines	Uncovered Line #s
All files	50.69	46.63	36.12	51.66

report-only-changed-files is enabled. No files were changed in this commit :)

[fernandatoledo]

"but in some cases it introduces some merge conflicts that GitHub's interface doesn't show as Merge Conflict in the Pull Request page."

Thank you so much for introducing this fix!!! 🚀 👏