chore: convert two slack channel ID char fields to foreign keys #2097

Job	Run time
Linting and tests / Lint entire project	1m 11s
Linting and tests / Lint database migrations	1m 9s
Linting and tests / Lint, test, and build frontend	1m 34s
Linting and tests / mypy	1m 25s
Linting and tests / Test technical documentation	18s
Linting and tests / Backend Tests: MySQL + RabbitMQ (RBAC enabled: True)	3m 35s
Linting and tests / Backend Tests: Plugin	34s
Linting and tests / Backend Tests: MySQL + RabbitMQ (RBAC enabled: False)	3m 39s
Linting and tests / Backend Tests: PostgreSQL + RabbitMQ (RBAC enabled: True)	1m 51s
Linting and tests / Backend Tests: PostgreSQL + RabbitMQ (RBAC enabled: False)	1m 57s
Linting and tests / Backend Tests: SQLite + Redis (RBAC enabled: True)	1m 45s
Linting and tests / Backend Tests: SQLite + Redis (RBAC enabled: False)	1m 41s
Linting and tests / Helm Chart Unit Tests	17s
Linting and tests / Unit tests - Migrators	25s
Snyk security scan / Snyk security scan	1m 27s
Linting and tests / Standard e2e tests (11.2.0) / Grafana: 11.2.0	4m 15s
Linting and tests / Standard e2e tests (10.3.0) / Grafana: 10.3.0	4m 24s
	31m 27s

Provide feedback