chore: add scorecard security scan

[ttosta-google]

Related to #11

[jackwotherspoon]

@ttosta-google for testing purposes you may want to make a commit to this PR branch enabling on pull_request trigger https://github.com/GoogleCloudPlatform/alloydb-java-connector/blob/add-scorecard-scan/.github/workflows/scorecard.yml#L16 to simply test that everything works. If the check works just revert the commit or make a new push to remove pull_request

[enocom]

Adding @jackwotherspoon as approver since he knows this the best.

[github-advanced-security]

This pull request sets up GitHub code scanning for this repository. Once the scans have completed and the checks have passed, the analysis results for this pull request branch will appear on this overview. Once you merge this pull request, the 'Security' tab will show more code scanning analysis results (for example, for the default branch). Depending on your configuration and choice of analysis tool, future pull requests will be annotated with code scanning analysis results. For more information about GitHub code scanning, check out the documentation.

[ttosta-google]

it worked! Thanks for the suggestion @jackwotherspoon