[terraform] Bump staging Identity to 0.51.1

Summary:

• Adds D14379 and D14380 to Identity 0.51 - these are follow ups and fixes to improved logs introduced in 0.51
• Introduced semver versioning. It's not worth bumping minor version for such small fixes

Test Plan: terraform plan

Reviewers: kamil, tomek

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D14392