MySQL查询结果增加同步延迟状态展示

[hhyo]

• 仅在出现延迟，即Seconds_Behind_Master>0时展示，null和0都不展示
• 多源复制的仅获取第一个Channel的延迟状态
• 查询账号需要授予REPLICATION CLIENT权限，否则不会展示
• 查看表结构不会展示

[codecov]

Codecov Report

Merging #303 into master will increase coverage by 0.02%.
The diff coverage is 93.75%.

@@            Coverage Diff             @@
##           master     #303      +/-   ##
==========================================
+ Coverage   85.05%   85.07%   +0.02%     
==========================================
  Files          66       66              
  Lines        8658     8672      +14     
==========================================
+ Hits         7364     7378      +14     
  Misses       1294     1294

Impacted Files	Coverage Δ
sql/engines/mysql.py	90.62% <100%> (+0.14%)	⬆️
sql/engines/tests.py	99.77% <100%> (ø)	⬆️
sql/tests.py	100% <100%> (ø)	⬆️
sql/utils/data_masking.py	98.02% <100%> (+0.02%)	⬆️
sql/query.py	53.95% <66.66%> (+0.67%)	⬆️

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