Cells: Fail DB configuration if TS is unreachable before sequence alteration

Overview

From gitlab-com/gl-infra/tenant-scale/cells-infrastructure/team#326 (comment 2571043467)

We could verify if TS is reachable and fail the process in case we face a network error. Maybe:

1. During gitlab:db:configure, we check if TS is available.
2. If not, we fail the process before configuring the schema.

During the cell provisioning, we call gitlab:db:configure, which calls alter_cell_sequences_range to alter DB sequences during for the cell. If TS is unreachable through TCP, the database is configured, but the sequences are not altered.

Deliverables

• When configuring the cell DB through gitlab:db:configure, fail the process case TS is unreachable through TCP client.
• Only when Gitlab.config.cell.enabled == true