### _Why are the changes needed?_
As described in #2887, random policy may cause task-hot-issues or production accident, so a POLLING balance policy is added to avoid this problem, we can "set kyuubi.engine.pool.balance.policy = POLLING" to use it.
### _How was this patch tested?_
- [x] Add some test cases that check the changes thoroughly including negative and positive cases if possible
- [] Add screenshots for manual tests if appropriate
- [x] [Run test](https://kyuubi.apache.org/docs/latest/develop_tools/testing.html#running-tests) locally before make a pull request
Closes#3662 from ychris78/epbp_1018.
Closes#2887
90834c1f [yuqi] fix bug
c0ce8a7e [yuqi] Fix typos
bec4ca13 [yuqi] Fix typos
dc4e3637 [yuqi] please add test case to cover the added methods
837c920b [yuqi] rename method getAndInc to getAndIncrement and modify the doc
02a8311f [yuqi] add getAndInc method and refer it
9436937d [yuqi] Improve configuration documentation
21b5d7d1 [yuqi] [KYUUBI #2887] Add a polling balance policy for spark engine pool Improve configuration documentation and delete useless comments
f0699b3c [yuqi] [KYUUBI #2887] Add a polling balance policy for spark engine pool
Authored-by: yuqi <1450636878@qq.com>
Signed-off-by: Fei Wang <fwang12@ebay.com>
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