make nameserver value of /etc/resolv.conf configurable

[lanefu]

add backwards-compatible defaults value to override contents of /etc/resolv.conf nameserver for those needing a workaround.

Description

programs like dig and nslookup parse /etc/resolv.conf directly and do not support the port attribute of nameserver host:port

this default var lets a user override to a value like 127.0.0.1 if the port isn't needed.

Related Issue

(https://github.com/mrlesmithjr/ansible-dnsmasq/issues/37)

as able to duplicate issue with latest debian

before

root@nanopi-r5s:/etc# dig google.com
dig: parse of /etc/resolv.conf failed

after

root@nanopi-r5s:/etc# dig google.com

; <<>> DiG 9.18.16-1-Debian <<>> google.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 61085
;; flags: qr rd ra; QUERY: 1, ANSWER: 6, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;google.com.                    IN      A

;; ANSWER SECTION:
google.com.             112     IN      A       142.251.163.139
google.com.             112     IN      A       142.251.163.113
google.com.             112     IN      A       142.251.163.101
google.com.             112     IN      A       142.251.163.138
google.com.             112     IN      A       142.251.163.100
google.com.             112     IN      A       142.251.163.102

;; Query time: 9 msec
;; SERVER: 127.0.0.1#53(127.0.0.1) (UDP)
;; WHEN: Tue Sep 05 23:52:20 UTC 2023
;; MSG SIZE  rcvd: 135

Types of changes

• [x ] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Checklist:

• [x ] I have read the CONTRIBUTING document.
• I have run the pre-merge tests locally and they pass.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.