duplicate validation by type, periodical resolving of targets DNS records

[Len4i]

• Add support for SRV record for target type of TCP (logic in readme)
• Add periodical (per ReloadConfig) resolving of targets DNS records for the case when IP may be changed dynamically (k8s mainly)
• Skip instead of fail on the not correct target (type mismatch or not resolvable DNS)
• Targets duplicate validation per target type instead of all list. So, you can add the same target for ICMP and HTTP tests