Add Knowledge Base tutorial: rollups with Materialized Views for time-series analytics

[Username46786]

This PR adds a new Knowledge Base article that demonstrates a common
ClickHouse design pattern: creating a rollup with Materialized Views
for fast time-series analytics.

The tutorial walks through:

• Raw events table (MergeTree) with partitioning, ORDER BY, TTL.
• Rollup table (AggregatingMergeTree) storing aggregate states.
• Materialized View to maintain rollups automatically.
• Queries using Merge vs FINAL, with EXPLAIN examples.
• Variations (daily rollups, codecs, TTL, backfilling).

Why:

• Rollups with MVs are one of the most frequently requested patterns
  by ClickHouse users.
• Provides an end-to-end, production-ready example that reduces the
  learning curve.
• Helps standardize a best-practice approach, reducing common Q&A
  traffic around time-series aggregation.

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[Blargian]

@Username46786 Thank you so much for this great contribution! I made a few minimal changes to formatting.