code insights: deploy TimescaleDB in Kubernetes deployments

[emidoots]

(See #17218 for general plan / explanation of the work being done on code insights.)

[github-actions]

Heads up @Joelkw @felixfbecker - the "team/code-insights" label was applied to this issue.

[emidoots]

• add codeinsights-db (TimescaleDB) deployment deploy-sourcegraph#1851
• insights: set POSTGRES_PASSWORD deploy-sourcegraph#1856
• codeinsights-db: remove liveness/readiness probes deploy-sourcegraph#1859
• frontend: configure codeinsights DB env var deploy-sourcegraph#1864
• https://github.com/sourcegraph/deploy-sourcegraph-dot-com/pull/4601
• https://github.com/sourcegraph/deploy-sourcegraph-dot-com/pull/4599