feat: adding coveralls integration

[willmendesneto]

Please check if the PR fulfills these requirements

• The commit messages follow our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (check one with "x")

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

Adding Coveralls Integration.

What is the current behavior? (You can link to an open issue here, add screenshots…)

What is the new behavior?
The pipeline will now collect the code coverage from our unit tests. It will be available on Coveralls link (added on README.md file)

Does this PR introduce a breaking change? (check one with "x")

• Yes
• No

If this PR contains a breaking change, please describe the impact and migration path for existing applications: …

Other information (if applicable):
N/A