fix: disable dynamic DNS service config

[rishtigupta]

PR Description:

• Based on the commit here, dynamic txt lookup for dns resolution flag is disabled by default in grpc-python.
• This commit explicitly disables it too.

tcpdump when running existing example without adding the flag explicitly:

sudo tcpdump -i any -vvv port 53 | grep -i cache.cell-alpha-dev.preprod.a.momentohq.com           ─╯
Password:
tcpdump: data link type PKTAP
tcpdump: listening on any, link-type PKTAP (Apple DLT_PKTAP), snapshot length 524288 bytes
    10.0.0.249.62558 > pd1nsc3.st.vc.shawcable.net.domain: [udp sum ok] 23436+ AAAA? cache.cell-alpha-dev.preprod.a.momentohq.com. (62)
    10.0.0.249.62558 > pd1nsc3.st.vc.shawcable.net.domain: [udp sum ok] 25894+ A? cache.cell-alpha-dev.preprod.a.momentohq.com. (62)
    pd1nsc3.st.vc.shawcable.net.domain > 10.0.0.249.62558: [udp sum ok] 23436 q: AAAA? cache.cell-alpha-dev.preprod.a.momentohq.com. 0/1/0 ns: cell-alpha-dev.preprod.a.momentohq.com. [15m] SOA ns-1810.awsdns-34.co.uk. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400 (146)
    pd1nsc3.st.vc.shawcable.net.domain > 10.0.0.249.62558: [udp sum ok] 25894 q: A? cache.cell-alpha-dev.preprod.a.momentohq.com. 1/0/0 cache.cell-alpha-dev.preprod.a.momentohq.com. [1m] A 54.186.170.81 (78)
    10.0.0.249.62558 > pd1nsc3.st.vc.shawcable.net.domain: [udp sum ok] 62957+ AAAA? cache.cell-alpha-dev.preprod.a.momentohq.com.local. (68)
    pd1nsc3.st.vc.shawcable.net.domain > 10.0.0.249.62558: [udp sum ok] 62957 NXDomain q: AAAA? cache.cell-alpha-dev.preprod.a.momentohq.com.local. 0/1/0 ns: . [10m54s] SOA a.root-servers.net. nstld.verisign-grs.com. 2025030402 1800 900 604800 86400 (143)
    pd1nsc3.st.vc.shawcable.net.domain > 10.0.0.249.56705: [udp sum ok] 49140 q: A? control.cell-alpha-dev.preprod.a.momentohq.com. 2/0/0 control.cell-alpha-dev.preprod.a.momentohq.com. [5m] CNAME cache.cell-alpha-dev.preprod.a.momentohq.com., cache.cell-alpha-dev.preprod.a.momentohq.com. [1m] A 54.186.170.81 (100)
    pd1nsc3.st.vc.shawcable.net.domain > 10.0.0.249.56705: [udp sum ok] 44100 q: AAAA? control.cell-alpha-dev.preprod.a.momentohq.com. 1/1/0 control.cell-alpha-dev.preprod.a.momentohq.com. [5m] CNAME cache.cell-alpha-dev.preprod.a.momentohq.com. ns: cell-alpha-dev.preprod.a.momentohq.com. [15m] SOA ns-1810.awsdns-34.co.uk. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400 (168)

Observe no txt lookups with current version of python sdk (v 1.25.0)

Relevant Research Links:

googleapis/gapic-generator#2817

Issue

https://github.com/momentohq/dev-eco-issue-tracker/issues/1132