Create GUI test for "Deploy key creation"

[wlsf82]

As a test pre-condition, the root user has to be authenticated.

Following is the page for the creation of a new public deploy key: http://localhost/admin/deploy_keys/new.

Remember to add the new test to the cypress/e2e/gui/allButProject.cy.js file, anywhere between the access token creation and deletion (preferably closer to another test of the same domain - admin/.)

If you need more information, don't hesitate to tag me (@wlsf82).

Also, remember to follow the project's contributing guidelines.

Cc. @Fabricioperrone.