fix: leader election should use different key with each application

[dk-lockdown]

ref: https://github.com/cectc/dbpack/issues/

Ⅰ. Describe what this PR did

Ⅱ. Does this pull request fix one issue?

Ⅲ. Why don't you add test cases (unit test/integration test)?

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov-commenter]

Codecov Report

Merging #130 (c25edee) into dev (a0a5bda) will not change coverage.
The diff coverage is n/a.

❗ Current head c25edee differs from pull request most recent head 1036873. Consider uploading reports for the commit 1036873 to get more accurate results

@@           Coverage Diff           @@
##              dev     #130   +/-   ##
=======================================
  Coverage   45.83%   45.83%           
=======================================
  Files          62       62           
  Lines        6351     6351           
=======================================
  Hits         2911     2911           
  Misses       3167     3167           
  Partials      273      273           

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[fatelei]

LGTM

[hzliangbin]

LGTM