roachtest: Skip flaky endpoint and fix retry logic for db-console/endpoints

This commit skips the rangelog endpoint on the admin server. This failure mode
is described in:
#148112 (comment)

This commit also sets an initial backoff when retrying endpoints. The default
of 50ms resulted in the 10 retries being exhausted too quickly. In mixed
version tests nodes are taken down and brought up, and so we observed many 404
failures due to this.

Fixes: #148187
Release note: None

Author: alyshanjahani-crl

pkg/cmd/roachtest/tests/db-console/admin_endpoints.json

@@ -78,6 +78,7 @@
     {
       "url": "/_admin/v1/rangelog",
       "method": "GET"
+      "skip": "https://github.com/cockroachdb/cockroach/pull/148112#issuecomment-2960322577"
     },
     {
       "url": "/_admin/v1/rangelog/{range_id}",

pkg/cmd/roachtest/tests/db_console_endpoints.go

@@ -248,7 +248,7 @@ func testEndpoint(
 		return nil
 	}
 
-	return withRetries(ctx, retry.Options{MaxRetries: 10}, f)
+	return withRetries(ctx, retry.Options{InitialBackoff: time.Second, MaxRetries: 10}, f)
 }
 
 // withRetries runs the given function f with the provided retry options.