Deploy the monitoring Vault policy

Summary:
Policy has been prepared, but not included for deployment.

This issue has been spotted by Vault credentials pillar test.

This is a follow-up for 21d127f52dc4

Ref T2123

Test Plan: (cd _tests && python -m unittest pillar/credentials/test_vault.py)

Reviewers: DorianWinty

Reviewed By: DorianWinty

Maniphest Tasks: T2123

Differential Revision: https://devcentral.nasqueron.org/D3664