Remove assertion from logging observers onConnectionSelected

Motivation:

If request is retried multiple times, `onConnectionSelected` callback
will be invoked multiple times (for every retry attempt) when logging
observers are applied at the client level.

Modifications:

- Remove `assert this.connInfo == null` from
`LoggingGrpcLifecycleObserver` and `LoggingHttpLifecycleObserver`;
- Clarify expectations in `HttpLifecycleObserver` javadoc;

Result:

No `AssertionError` in tests that can retry.

servicetalk-grpc-utils/src/main/java/io/servicetalk/grpc/utils/LoggingGrpcLifecycleObserver.java

@@ -84,7 +84,6 @@ private LoggingGrpcExchangeObserver(final FixedLevelLogger logger) {
 
         @Override
         public void onConnectionSelected(final ConnectionInfo info) {
-            assert this.connInfo == null;
             this.connInfo = info;
         }
 

servicetalk-http-api/src/main/java/io/servicetalk/http/api/HttpLifecycleObserver.java

@@ -39,6 +39,9 @@ public interface HttpLifecycleObserver {
 
     /**
      * Callback when a new HTTP exchange starts.
+     * <p>
+     * Depending on the order in which the observer is applied, this callback can be invoked either for every retry
+     * attempt (if an observer is added after retrying filter) or only once per exchange.
      *
      * @return an {@link HttpExchangeObserver} that provides visibility into exchange events
      */
@@ -56,6 +59,8 @@ interface HttpExchangeObserver {
 
         /**
          * Callback when a connection is selected for this exchange execution.
+         * <p>
+         * This callback may be invoked for every retry attempt.
          *
          * @param info {@link ConnectionInfo} of the selected connection
          */

servicetalk-http-utils/src/main/java/io/servicetalk/http/utils/LoggingHttpLifecycleObserver.java

@@ -81,7 +81,6 @@ private LoggingHttpExchangeObserver(final FixedLevelLogger logger) {
 
         @Override
         public void onConnectionSelected(final ConnectionInfo info) {
-            assert this.connInfo == null;
             this.connInfo = info;
         }