Configuration for setting maximum number of connection pools to be created

[jchenga]

Introduce a configuration option to specify the maximum number of connection pools a ConnectionProvider should create. Once the maximum number is exceeded, a warning message is logged.

Fixes #3318.

[violetagg]

@jchenga Thanks for the PR!
I do have some suggestions for the name of the new API and for the tests.

[jchenga]

I have made the suggested changes.

[violetagg]

Why do we want to allow this value to be set to 0? If one doesn't want pooling, one can disable the pooling.

[violetagg]

Please add a check for the provided value.

[violetagg]

Do we want the user to be able to reset this to -1? For example:

reactor-netty/reactor-netty-core/src/main/java/reactor/netty/resources/ConnectionProvider.java

Lines 585 to 602 in 11f91b0

	/**
	* Set the options to use for configuring {@link ConnectionProvider} the maximum number of registered
	* requests for acquire to keep in a pending queue
	* When invoked with -1 the pending queue will not have upper limit.
	* Default to {@code 2 * max connections}.
	*
	* @param pendingAcquireMaxCount the maximum number of registered requests for acquire to keep
	* in a pending queue
	* @return {@literal this}
	* @throws IllegalArgumentException if pendingAcquireMaxCount is negative
	*/
	public final SPEC pendingAcquireMaxCount(int pendingAcquireMaxCount) {
	if (pendingAcquireMaxCount != -1 && pendingAcquireMaxCount <= 0) {
	throw new IllegalArgumentException("Pending acquire max count must be strictly positive");
	}
	this.pendingAcquireMaxCount = pendingAcquireMaxCount;
	return get();
	}

[violetagg]

Let's dispose the ConnectionProvider here.
No need to dispose the server it will be disposed by reactor.netty.BaseHttpTest#disposeServer