Add prettirer PR check

[dmytro-ndp]

What does this PR do?

This PR adds a check for prettier formatting violations to the smoke test GitHub Action workflow. This will ensure code quality and consistent formatting across the codebase.

Change list:

1. Added a prettier:check script to the e2e tests package.json
2. Added a "Check prettier rules" step to the PR check workflow

Benefit: catches formatting inconsistencies early in the development process.

Screenshot/screencast of this PR

What issues does this PR fix or reference?

#23508

How to test this PR?

• Verify that the CI pipeline runs the prettier check successfully
• Test with intentionally malformatted code to ensure it fails correctly
• Confirm that running npm run prettier fixes the issues

Example of prettier check failure:
https://github.com/eclipse-che/che/actions/runs/16735722106/job/47374004942

Warning: Prettier formatting issues found in the following files:
Warning: [warn] pageobjects/git-providers/OauthPage.ts
Run 'cd tests/e2e && npm run prettier' to fix formatting issues.
Error: Prettier check failed! Please fix the formatting issues.
Error: Process completed with exit code 1.

Example of successful run of prettier check:
https://github.com/eclipse-che/che/actions/runs/16735886970

Running prettier check...
No prettier formatting issues found.

PR Checklist

As the author of this Pull Request I made sure that:

• The Eclipse Contributor Agreement is valid
• Code produced is complete
• Code builds without errors
• Tests are covering the bugfix or new feature
• The repository devfile is up to date and works
• Sections What issues does this PR fix or reference and How to test this PR completed
• Relevant user documentation updated
• Relevant contributing documentation updated
• CI/CD changes implemented, documented and communicated

Reviewers

Reviewers, please comment how you tested the PR when approving it.

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