[client] Expose node resources and table sizes

[fkzhao]

Purpose

Add node resource information and table data size statistics to the Fluss Java Client.

Linked issue: close #xxx

Brief change log

• Add CPU, memory, and data disk information to ServerNode.
• Add NodeResourceInfo for exposing node resource snapshots.
• Make Admin#getServerNodes() return Coordinator and TabletServer nodes with resource information.
• Add Prometheus metrics for node CPU, memory, and data disk usage.
• Rename internal resource information RPC to GetServerInfoRequest/Response.
• Remove the obsolete ServerMetrics client API.
• Add table data size to TableStats.
• Add TableInfoWithStats and Admin#listTableDetails(String).
• Update Java Client documentation and examples.

Tests

• FlussAdminITCase#testGetServerNodes
• FlussAdminITCase#testGetTableStatsForLogTable
• FlussAdminITCase#testGetTableStatsForPrimaryKeyTableWithFailover
• FlussAdminITCase#testListTableDetailsIncludesTableStats
• ServerNodeTest
• TabletServerResourceProbeTest
• mvn -pl fluss-client -am -DskipTests test-compile
• mvn -pl fluss-flink/fluss-flink-common -am -DskipTests test-compile
• mvn spotless:check -pl fluss-rpc,fluss-client,fluss-server

API and Format

• Admin#getServerNodes() returns all currently available Coordinator and TabletServer nodes.
• ServerNode#resourceInfo() exposes:
  • CPU core count
  • Total memory
  • Current CPU usage
  • Used memory
  • Total and used data disk space
  • Collection timestamp
• TableStats#getDataSizeBytes() exposes the local physical data size of a table.
• Admin#listTableDetails(String) returns table metadata together with current table statistics.
• Node resource information is queried directly from Fluss nodes and is independent of Prometheus querying.
• The RPC API key remains unchanged.

Documentation

• Update the Java Client documentation with examples for:
  • Querying node resource information
  • Querying table data size
  • Listing table metadata together with statistics
• Add the ServerInfoClientExample example.