Add docs about additional config settings for disagg arch

Enhancement

profiles.default.dt_read_thread_count_scale
2.0, "Number of read thread = number of logical cpu cores * dt_read_thread_count_scale.  Only has meaning at server startup."

profiles.default.io_thread_count_scale
5.0, "Number of thread of IOThreadPool = number of logical cpu cores * io_thread_count_scale.  Only has meaning at server startup."

profiles.default.init_thread_count_scale
100, "Number of thread = number of logical cpu cores * init_thread_count_scale. It just works for thread pool for initStores and loadMetadata. Only has meaning at server startup."

profiles.default.remote_gc_method
1, "The method of running GC task on the remote store. 1 - lifecycle, 2 - scan."

profiles.default.remote_gc_interval_seconds
3600, "The interval of running GC task on the remote store. Unit is second."

profiles.default.remote_gc_min_age_seconds
3600, "The file will NOT be compacted when the time difference between the last modification is less than this threshold"

profiles.default.remote_gc_ratio
0.5, "The files with valid rate less than this threshold will be compacted"

profiles.default.dt_filecache_max_downloading_count_scale
1.0, "Max downloading task count of FileCache = io thread count * dt_filecache_max_downloading_count_scale."

profiles.default.dt_filecache_min_age_seconds
1800, "Files of the same priority can only be evicted from files that were not accessed within `dt_filecache_min_age_seconds` seconds."

profiles.default.disagg_build_task_timeout
DEFAULT_DISAGG_TASK_BUILD_TIMEOUT_SEC, "disagg task establish timeout, unit is second."

profiles.default.disagg_task_snapshot_timeout
DEFAULT_DISAGG_TASK_TIMEOUT_SEC, "disagg task snapshot max endurable time, unit is second."

profiles.default.disagg_fetch_pages_timeout
DEFAULT_DISAGG_FETCH_PAGES_TIMEOUT_SEC, "fetch disagg pages timeout for one segment, unit is second."