[cassandra] Add Configuration.Close() to ensure TLS cert watcher is c…

…losed (jaegertracing#4515)

Which problem is this PR solving?
Resolves jaegertracing#4514

Short description of the changes
Implement a Close Function in Cassandra to allow us to close the
leaky-go routine.

Signed-off-by: kennyaz <115052215+kennyaz@users.noreply.github.com>
Co-authored-by: Yuri Shkuro <yurishkuro@users.noreply.github.com>
Signed-off-by: KevinSchneider <kevin.schneider@target.com>

pkg/cassandra/config/config.go

@@ -163,6 +163,10 @@ func (c *Configuration) NewCluster(logger *zap.Logger) (*gocql.ClusterConfig, er
 	return cluster, nil
 }
 
+func (c *Configuration) Close() error {
+	return c.TLS.Close()
+}
+
 func (c *Configuration) String() string {
 	return fmt.Sprintf("%+v", *c)
 }