Add functional and entity checks for SLAs

These steps are able to bypass the check:
1. Login as Admin
2. Create a new SLA
3. Copy the JSON rest model for the SLA
4. Login as a user who doesn't have access to a feed used by the SLA
5. Call POST /v1/feedmgr/sla with the JSON rest model for the SLA

Expected result:
The call fails with access denied exception.

Actual result:
The call succeeds and the SLA is updated.

The check is also not done for:

good catch.. i will fix the first issue.
The Assessments is a known item. I dont have access checks around that yet

created to track the 1 outstanding issue. Closing this jira