Improve error message in REST Client when no matching readers found #35960

Job	Run time
Attach pull request number	3s
CI Sanity Check	32s
Initial JDK 17 Build	9m 51s
Calculate Test Jobs	9s
JVM Tests - JDK 17	27m 27s
JVM Tests - JDK 21	36m 31s
Gradle Tests - JDK ${{ matrix.java.name }}	0s
Devtools Tests - JDK ${{ matrix.java.name }}	0s
JVM Tests - JDK 17 Windows	40m 41s
Maven Tests - JDK ${{ matrix.java.name }}	0s
Quickstarts Compilation - JDK 17	5m 54s
Native Tests - Virtual Thread - Main	3m 18s
Kubernetes Tests - JDK ${{ matrix.java.name }}	0s
Native Tests - Virtual Thread - Messaging	9m 48s
MicroProfile TCKs Tests	8m 42s
Native Tests - Main	7m 22s
Native Tests - Data3	4m 42s
Native Tests - Data4	5m 18s
Native Tests - Messaging1	15m 37s
Native Tests - Security2	8m 24s
Native Tests - Security3	6m 1s
Native Tests - Cache	9m 19s
Native Tests - HTTP	21m 31s
Native Tests - Misc1	9m 45s
Native Tests - Misc3	4m 53s
Native Tests - Misc4	9m 23s
Native Tests - gRPC	4m 56s
Build report	13s
	4h 10m 20s

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