Revert "embed: fix HTTPs + DNS SRV discovery"

[gyuho]

In 3.2.8, both configurations work with TLS/SRV

"hosts": [
  "m1.etcd.local",
  "m2.etcd.local",
  "m3.etcd.local",
  "etcd.local",
  "127.0.0.1",
  "localhost"
]

"hosts": [
  "*.etcd.local",
  "etcd.local",
  "127.0.0.1",
  "localhost"
]

In 3.2.9, we added wildcard to peer server name (e.g. *.etcd.local when DNS cluster is etcd.local).

Now the first configuration doesn't work

"hosts": [
  "m1.etcd.local",
  "m2.etcd.local",
  "m3.etcd.local",
  "etcd.local",
  "127.0.0.1",
  "localhost"
]

Second configuration still works

"hosts": [
  "*.etcd.local",
  "etcd.local",
  "127.0.0.1",
  "localhost"
]

But, not every tool supports wildcard certs.

We are reverting this change, also in upcoming patch release 3.2.10.

Address #8445 and #8798.
Reverts #8651.

[xiang90]

we need to update the documentation to make it clear that the TLS certs for DNS discovery must include the root domain in SAN to prevent mitm attack.

[gyuho]

@xiang90 I've highlighted this change in CHANGELOG and security.md.

PTAL.

[xiang90]

lgtm

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@6260df7). Click here to learn what that means.
The diff coverage is 0%.

@@            Coverage Diff            @@
##             master    #8884   +/-   ##
=========================================
  Coverage          ?   76.19%           
=========================================
  Files             ?      359           
  Lines             ?    29721           
  Branches          ?        0           
=========================================
  Hits              ?    22646           
  Misses            ?     5504           
  Partials          ?     1571

Impacted Files	Coverage Δ
embed/config.go	61.63% <0%> (ø)

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