Add Inputs to sharing model

## What?

From support issue: https://github.com/Graylog2/support/issues/294
[gz#2372](https://graylog7416.zendesk.com/agent/tickets/2372)

Manage permissions of users to allow create/manage pipelines for specific inputs. They should also be able to manage global grok patterns, if possible.

## How is it working currently:
Currently it's not possible to manage permissions for users so they can create and mange pipelines for specific inputs

## Intended Purpose:
Manage permissions of users to allow create/manage pipelines for specific inputs. They should also be able to manage global grok patterns, if possible.

## Expected Outcome:
Users are allowed to create and manage pipelines for specific inputs to which they have permissions.