[BOT-103] Fetch only new warnings

[miguelcarreiro]

Description

This pull request addresses issue BOT-103.

Note: A new issue was created (#103) to better represent the PR purpose (the old issue was #98). Since GitHub don't have an option to rename branch, I decided to keep the old branch name, changing only PR description to reference new issue.

Task items:

• [x] Add sequelize configurations;
• [ ] Add database model;
• [ ] Save warnings;
• [ ] Announce only new warnings.

Requirements

Requirements when deploying the current work to an environment (dev, staging or production):

• Install new dependencies.

[miguelcarreiro]

@ClaudioVarandas was assigned to issue #103, so this PR will be closed.