domain, store/tikv: enable etcd client auto sync

[disksing]

Signed-off-by: disksing i@disksing.com

What problem does this PR solve?

When all PD nodes are replaced by new PD nodes, etcd clients (used by DDL worker and safepoint syncer) in tidb will lost connection with PD cluster.

What is changed and how it works?

Enable etcd's AutoSync feature so it will automatically update member list.

Check List

Tests

• Manual test (add detailed scripts or steps below)

1. start a cluster with 3 PDs, 1 TiKV, 1TiDB
2. Join 3 more PDs then member delete original 3 PDs.
3. Wait 100s and check if there are any 'safePoint out of sync' errors (TRUE for master, FALSE for auto-sync)
4. Run some DDL and check if it succeds (FALSE for master, TRUE for auto-sync)

Note: No unit test case included, it will be more suitable to add a integration test in schrodinger later. This bug is kind urgent and the fix is straightforward so I guess we can merge it ahead.

Related changes

• Need to cherry-pick to the release branch
• Need to be included in the release note

[codecov-io]

Codecov Report

Merging #9575 into master will decrease coverage by <.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #9575      +/-   ##
==========================================
- Coverage    67.3%   67.29%   -0.01%     
==========================================
  Files         376      376              
  Lines       78961    78963       +2     
==========================================
- Hits        53144    53139       -5     
- Misses      21058    21061       +3     
- Partials     4759     4763       +4

Impacted Files	Coverage Δ
store/tikv/kv.go	53.52% <0%> (-0.26%)	⬇️
domain/domain.go	40.24% <0%> (-0.08%)	⬇️
ddl/delete_range.go	75.13% <0%> (-4.24%)	⬇️
store/tikv/gcworker/gc_worker.go	41.57% <0%> (+0.42%)	⬆️

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[zimulala]

LGTM

[nolouch]

LGTM