write e2e test of project join request email workflow

[hahn-kev]

users can now request to join a project thanks to #258, since this is an email workflow feature we would like to have automated tests for it.

the test should verify the manager receives an email and can add the user to the project by clicking it. Once the test is finished the user should be removed from the project to ensure the test can be run again, this could be tricky as it requires a user to be an org member. I'm not sure the best way to handle this as using an existing user could cause race conditions with other tests that might expect the user not to be a member of an existing project.

[rmunn]

Now that #1390 exists and is likely to be merged soon, this should test both the button in the "new project" page and also the button available on the project page (visible to org members who aren't project members) that #1390 adds.