XXX software/dnsresolver: Introduce

XXX:
 * cover with tests
 * split to stack to eventually use the local v4 access
 * add proper README.rst
 * add missing udp listening promise
Status Job ID Name Coverage
  External
passed SlapOS.SoftwareReleases.IntegrationTest-luke/feature/dnsresolver

01:34:55

running SlapOS.SoftwareReleases.IntegrationTest-luke/feature/dnsresolver

10217:54:26

passed SlapOS.SoftwareReleases.IntegrationTest-luke/feature/dnsresolver

01:30:01

passed SlapOS.SoftwareReleases.IntegrationTest-luke/feature/dnsresolver

01:35:54

passed SlapOS.SoftwareReleases.IntegrationTest-luke/feature/dnsresolver

02:54:47