Do not set 'realm=Quarkus' in Basic auth challenge

[sberyozkin]

Fixes #27291

Currently, reporting an optional realm property in the Basic auth chalenge WWW-Authenticate: Basic realm="Quarkus" by default has 2 problems: 1) it affects the clients which are not prepared/expect a realm property as reported on Zulip and 2) it leaks an implementation detail, a minor case of the information exposure.

So this PR simply makes a quarkus.http.realm property optional for the realm reported only if it is required. It is really a bug fix so proposing a backport as well

[quarkus-bot]

Failing Jobs - Building c8843a7

Status	Name	Step	Failures	Logs	Raw logs
✔️	JVM Tests - JDK 11
✖	JVM Tests - JDK 11 Windows	Build	Failures	Logs	Raw logs
✔️	JVM Tests - JDK 17
✔️	JVM Tests - JDK 18

Full information is available in the Build summary check run.

Failures

⚙️ JVM Tests - JDK 11 Windows #

- Failing: extensions/vertx-http/deployment 
! Skipped: extensions/agroal/deployment extensions/amazon-lambda-http/deployment extensions/amazon-lambda-rest/deployment and 309 more

📦 extensions/vertx-http/deployment

✖ io.quarkus.vertx.http.http2.Http2Test.testHttp2EnabledSsl line 57 - More details - Source on GitHub

java.util.concurrent.ExecutionException: javax.net.ssl.SSLHandshakeException: Failed to create SSL connection
	at java.base/java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:395)
	at java.base/java.util.concurrent.CompletableFuture.get(CompletableFuture.java:1999)