Update -memberlist.join flag to use DNS-SD format

[dimitarvdimitrov]

What this PR does

The default value for -memberlist.join in jsonnet and helm does not use DNS service-discovery format. Without using this format, the change in grafana/dskit#195 will not result in fast joining. The resolution in dskit will not resolve the -memberlist.join address. Instead, resolution will be left to the memberlist library. Memberlist will resolve to pod IPs and will effectively join all nodes during the supposed "fast-join" phase.

Which issue(s) this PR fixes or relates to

Fixes #

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[pstibrany]

Thanks for spotting the problem. I confirm that dns+... format helps memberlist KV's fast-join operation to work correctly.

Correct output is:

level=info ts=2022-07-26T14:58:42.373220881Z caller=memberlist_client.go:545 msg="memberlist fast-join starting" nodes_found=37 to_join=8
...
level=info ts=2022-07-26T14:58:42.45983464Z caller=memberlist_client.go:565 msg="memberlist fast-join finished" joined_nodes=8 elapsed_time=102.926227ms

(nodes_found=37 and joined_nodes=8 is correct for "fast-join")

Previously wrong output:

level=info ts=2022-07-25T13:42:29.567761114Z caller=memberlist_client.go:545 msg="memberlist fast-join starting" nodes_found=1 to_join=4
...
level=info ts=2022-07-25T13:42:29.913222231Z caller=memberlist_client.go:565 msg="memberlist fast-join finished" joined_nodes=34 elapsed_time=345.466911ms

(nodes_found=1 and joined_nodes=34 is wrong)