[issues-7892] add e2e test to verify a new tenant would be queryable

[jnyi]

This e2e test validates new tenant would open a separate TSDB: thanos-io#7892

especially logs would indicate:

ts=2024-11-13T06:33:34.121916792Z caller=multitsdb.go:697 level=info name=pantheon-db component=receive component=multi-tsdb tenant=random-tenant123 msg="opening TSDB"
ts=2024-11-13T06:33:34.128508813Z caller=multitsdb.go:743 level=info name=pantheon-db component=receive component=multi-tsdb tenant=random-tenant123 msg="TSDB is now ready"

• I added CHANGELOG entry for this change.
• Change is not relevant to the end user.

Changes

Verification