Add support for read-only access to projects

### Problem Statement

**Problem**

In large organizations some users need to view issues and especially dashboards related to the overall performance of a project. However, the current IAM system in Sentry requires they have read/write access as a "Contributor". This role allows grants write access to issues and is not appropriate for users who just need to view issues and dashboards.

**Proposed Solution**

Currently there are only two per-project user roles: "Team Contributor" and "Team Admin". Both have the following permission:

> Can view and act on issues (such as assigning and resolving)

(see the [Permissions](https://docs.sentry.io/organization/membership/#permissions-1) documentation)

User roles are assigned as part of a team membership so to solve this use case it appears that a new "Team Viewer" team role should be added. This role should just have permissions to view issues and dashboards but not alter or interact with the project in any other way.

**Alternative (or additional) Solution**

Add dashboard permissions that are distinct from the projects that they source data from would also help. This may be a good feature to have in addition to adding a new "Team Viewer" role. Large organizations will likely create three teams for every project `myproject-contributors`, `myproject-admins`, and `myproject-guests` and if distinct dashboard permissions were an option some projects may wish to only add the `myproject-guests` to the dashboards and not the project itself.

### Solution Brainstorm

_No response_

### Product Area

Unknown