add validation for cloud storage cache size to be a multiple of segment size

[abhijat]

Who is this for and what problem do they have today?

when tiered storage/SI is used in redpanda, the cloud storage cache needs to be set up to be some size so that it can hold multiple segments. We should validate that the size is at least 10x the segment size.

What are the success criteria?

The application startup validates that the cloud storage cache is at least 10x the segment size.

Why is solving this problem impactful?

The cloud storage cache undergoes segment eviction if it is full. With a cache smaller than a single segment, it is possible for each read to cause an eviction negatively affecting performance.

Additional notes

The current documentation suggests a minimum cloud storage cache size of 20 GB.

[jcsp]

I think we'll end up doing https://github.com/redpanda-data/core-internal/issues/374 to avoid the need for the cache to be this large before we get around to this ticket.