Fix "too many open files" error when running integration tests

[adutra]

This was due to the fact that each token fetch created a new client, and the client wasn't closed.

The typical stack trace is:

failed to open a new selector
io.netty.channel.ChannelException: failed to open a new selector
	at app//io.netty.channel.nio.NioEventLoop.openSelector(NioEventLoop.java:179)
...
	at app//org.apache.polaris.service.it.ext.PolarisServerManager.createClient(PolarisServerManager.java:64)
	at app//org.apache.polaris.service.it.ext.PolarisServerManager.accessManager(PolarisServerManager.java:55)
	at app//org.apache.polaris.service.it.env.PolarisClient.obtainToken(PolarisClient.java:118)
	at app//org.apache.polaris.service.it.env.PolarisClient.managementApi(PolarisClient.java:88)
	at app//org.apache.polaris.service.it.env.PolarisClient.cleanUp(PolarisClient.java:126)
...
Caused by: java.io.IOException: Too many open files
	at java.base/sun.nio.ch.KQueue.create(Native Method)
	at java.base/sun.nio.ch.KQueueSelectorImpl.<init>(KQueueSelectorImpl.java:83)
	at java.base/sun.nio.ch.KQueueSelectorProvider.openSelector(KQueueSelectorProvider.java:36)
	at io.netty.channel.nio.NioEventLoop.openSelector(NioEventLoop.java:177)
	... 32 more

[snazy]

Heh, nice catch

[dimas-b]

Nice catch. Sorry I missed it when I added PolarisAccessManager 🤦