Update UnboundID LDAP SDK to 6.0.3

[tvernum]

The new release contains fixes for leaking threads (see #80305) and
bias in round robin server sets, both of which are relevant to
Elasticsearch security.

Resolves: #80305

[elasticmachine]

Pinging @elastic/es-security (Team:Security)

[ywangd]

LGTM

Do we want to remove this special handling for 6.0.2?

elasticsearch/x-pack/plugin/security/src/test/java/org/elasticsearch/xpack/security/authc/ldap/support/SessionFactoryLoadBalancingTests.java

Lines 203 to 211 in 647e5fe

	if (com.unboundid.ldap.sdk.Version.getShortVersionString().equals("unboundid-ldapsdk-6.0.2")) {
	// This is the behaviour in 6.0.2, but per it should be fixed in 6.0.3
	// See: https://github.com/pingidentity/ldapsdk/issues/118
	// See: https://github.com/pingidentity/ldapsdk/commit/2d08c5258c3a62b7c90cd4e878c4a0d25ae01a82
	ports.forEach(port -> {
	int count = bindCountPerPort.get(port).get();
	assertThat("Connections to port [" + port + "]", count, greaterThanOrEqualTo(numberOfIterations));
	assertThat("Connections to port [" + port + "]", count, lessThanOrEqualTo(numberOfIterations * (1 + numberToKill)));
	});

[tvernum]

Do we want to remove this special handling for 6.0.2?

Yes, but I want to get the upgrade done as a standalone piece so we can close #80305 and then come back and cleanup.

If it resolve #80305 then we can also remove some of the attempted workaround in there.

[elasticsearchmachine]

💚 Backport successful

Status	Branch	Result
✅	8.0