Convert table names to const

Summary:
Made changes according to: https://linear.app/comm/issue/ENG-707/convert-table-names-to-const
Changed all tableName fields to const.
Fixed getters so they are alcos const.
Changed naming convention so it match other constants in those files.

Test Plan:
Run backup and block services locally in docker.
Run integration tests for both - they passed.

Reviewers: tomek, inka, kamil, atul, jon

Reviewed By: tomek

Subscribers: abosh, atul, kamil, inka, ashoat, tomek

Differential Revision: https://phab.comm.dev/D5473