bootstrapper: only err if no control plane IPs available (#3496)

Previously we errored out of the entire join if retrieval
of either LB IP or control plane public IP failed. This resulted
in the entire "use either IP" logic not working as intended. This now
makes it log a warning only if the IP retrievals fail, and only errors
out of the join if no IP can be found at all.

bootstrapper/internal/joinclient/joinclient.go

@@ -173,13 +173,13 @@ func (c *JoinClient) tryJoinWithAvailableServices() (ticket *joinproto.IssueJoin
 
 	endpoint, _, err := c.metadataAPI.GetLoadBalancerEndpoint(ctx)
 	if err != nil {
-		return nil, nil, fmt.Errorf("failed to get load balancer endpoint: %w", err)
+		c.log.Warn("Failed to get load balancer endpoint", "err", err)
 	}
 	endpoints = append(endpoints, endpoint)
 
 	ips, err := c.getControlPlaneIPs(ctx)
 	if err != nil {
-		return nil, nil, fmt.Errorf("failed to get control plane IPs: %w", err)
+		c.log.Warn("Failed to get control plane IPs", "err", err)
 	}
 	endpoints = append(endpoints, ips...)