[Config]Allower use to config different thrift server model

[WingsGo]

Doris only support TThreadPoolServer model in thrift server, but the server model is not effective in some high concurrency scenario, and the server model is not easy to solve high concurrency scenario.So I propsal to introduced a new config to allower use to choose different server model by their scenario, and we can add more server model when there is a need.

[WingsGo]

There is an article discuss about different Thrift Server model https://www.codelast.com/%E5%8E%9F%E5%88%9B%EF%BC%88%E7%BF%BB%E8%AF%91%EF%BC%89java%E7%89%88%E7%9A%84%E5%90%84%E7%A7%8Dthrift-server%E5%AE%9E%E7%8E%B0%E7%9A%84%E6%AF%94%E8%BE%83/