Avoid create duplicated access requests

[wallrony]

Is your feature request related to a problem? Please describe.
Currently is possible to create more than one access request for a resource or role at the same time (before the first stales).

Describe the solution you'd like
Add a validation to verify if the user already has a pending request for that resource or role.

[camposer]

If we proceed to implement this, then the user should be enabled to read all the pending access requests. Maybe we can create a new command that gives you show access requests and then enable this feature.