### Why I did it
Fix the issue detected by[ TestStaticMgmtPortIP::test_dynamic_dns_not_working_when_static_ip_configured ](https://github.com/sonic-net/sonic-mgmt/blob/master/tests/dns/static_dns/test_static_dns.py#L105C9-L105C63) test.
### How I did it
Query MGMT interface configuration. Do not apply dynamic DNS configuration when MGMT interface has static IP address.
#### How to verify it
Run `tests/dns/static_dns/test_static_dns.py` sonic-mgmt tests.
- Why I did it
Add support for static DNS configuration. According to sonic-net/SONiC#1262 HLD.
- How I did it
Add a new resolv-config.service that is responsible for transferring configuration from Config DB into /etc/resolv.conf file that is consumed by various subsystems in Linux to resolve domain names into IP addresses.
- How to verify it
Run the image compilation. Each component related to the static DNS feature is covered with the unit tests.
Run sonic-mgmt tests. Static DNS feature will be covered with the system tests.
Install the image and run manual tests.
- Why I did it
fixes#12907
When the management interface IP address configuration changes from dynamic to static the DNS configuration (retrieved from the DHCP server) in /etc/resolv.conf remains uncleared. This leads to a DNS configuration pointing to the wrong nameserver. To make the behavior clear DNS configuration received from DHCP should be cleared.
- How I did it
Use resolvconf package for managing DNS configuration. It is capable of tracking the source of DNS configuration and puts the configuration retrieved from the DHCP servers into a separate file. This allows the implementation of DNS configuration cleanup retrieved from DHCP during networking reconfiguration.
- How to verify it
Ensure that the management interface has no static configuration.
Check that /etc/resolv.conf has DNS configuration.
Configure a static IP address on the management interface.
Verify that /etc/resolv.conf has no DNS configuration.
Remove the static IP address from the management interface.
Verify that /etc/resolv.conf has DNS configuration retrieved form DHCP server.
Why I did it
nameserver and domain entries from build system fsroot gets into sonic image.
How I did it
Clear /etc/resolv.conf before building image
How to verify it
Built image with it and verified with install that /etc/resolv.conf is empty
