raft: ensure CheckQuorum is enabled when readonlyoption is lease based

[xiang90]

Fix #8450

The previous behavior is to return 0(invalid) index if CheckQuroum is not enabled but ReadOnlyOption is lease based.

This commit makes the checking explicitly during the initialization phase.

[xiang90]

/cc @javaforfun

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@085adc5). Click here to learn what that means.
The diff coverage is 33.33%.

@@            Coverage Diff            @@
##             master    #8567   +/-   ##
=========================================
  Coverage          ?   75.55%           
=========================================
  Files             ?      356           
  Lines             ?    29152           
  Branches          ?        0           
=========================================
  Hits              ?    22027           
  Misses            ?     5567           
  Partials          ?     1558

Impacted Files	Coverage Δ
raft/raft.go	92.29% <33.33%> (ø)

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[lishuai87]

LGTM