[TASK] Implement cache region list and statistics endpoints

[hassandotcms]

Description

Implement two endpoints in CacheResource.java for the Maintenance portlet Cache tab: one to list cache region names (for the flush dropdown) and one to return cache statistics (JVM memory + per-provider per-region hit/miss/size data).

Acceptance Criteria

GET /v1/caches

• API caller must receive an alphabetically sorted list of all cache region names
• Response must use standard ResponseEntityView wrapper
• Must require backend user with Maintenance portlet access

GET /v1/caches/stats

• API caller must receive JVM memory information: maxMemory, allocatedMemory, usedMemory, freeMemory (as raw long values in bytes)
• API caller must receive a list of cache providers, each containing: providerName, column names, and per-region statistics
• Per-region statistics must include all columns from CacheProviderStats.getStatColumns() with values from CacheStats.getStatValue(col)
• Must require backend user with Maintenance portlet access

Priority

None

Additional Context

• Region names come from CacheLocator.getCacheIndexes() — returns Object[], cast each to String and sort
• Cache stats come from CacheLocator.getCacheAdministrator().getCacheStatsList() — returns List<CacheProviderStats>
• Each CacheProviderStats has getProviderName(), getStatColumns() (LinkedHashSet), and getStats() (List of CacheStats)
• JVM memory: Runtime.getRuntime().maxMemory(), .totalMemory(), .freeMemory()

[github-actions]

PRs linked to this issue

• Implement Cache Management Apis #35190 by @hassandotcms