[CIVIS-3172] use repository name as default test service name

[anmarchenko]

What does this PR do? In order to simplify onboarding for new customers it provides better default service name when none is provided.

Additional Notes

• last segment of git remote URL is used as a repository name
• as a fallback, current folder is used (where git repo is located)

How to test the change? Unit tests are provided.

Example project without service name configured: https://github.com/anmarchenko/sidekiq/tree/anmarchenko/datadog-ci-visibility

Service is set to repository name:

[codecov-commenter]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (c56656c) 99.15% compared to head (f8e5691) 99.11%. Report is 5 commits behind head on main.

Files	Patch %	Lines
lib/datadog/ci/utils/git.rb	84.61%	2 Missing :warning:
...adog/ci/contrib/cucumber/configuration/settings.rb	66.66%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #104 +/- ## ========================================== - Coverage 99.15% 99.11% -0.05% ========================================== Files 147 147 Lines 6289 6338 +49 Branches 264 269 +5 ========================================== + Hits 6236 6282 +46 - Misses 53 56 +3 ```

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