新增密码仓库的初步支持

[LeoQuote]

有些云厂商或公司内部设置了密码自动轮换, 保证安全, archery 的密码只能是静态的, 只能通过外挂程序来更新数据库内的密码, 本PR带来一个新的功能, 可以在 engine 初始化时自动去请求数据库的账号名和密码, 达到相对的安全.

同时提供了对应的配置项, 供高级使用者提供自己的密码管理器实现, 其中的实现可以完全自己掌控

1. 新增 DummyMixin , 作为base
2. 新增 VaultMixin, 作为范例
3. 配置项中新增 PASSWORD_MIXIN_PATH, 供需要的用户覆盖内置的密码管理器, 替代为自行实现的KMS, 如各大云厂商提供的KMS.

replace #2212

[codecov]

Codecov Report

Attention: Patch coverage is 87.93103% with 7 lines in your changes missing coverage. Please review.

Project coverage is 78.43%. Comparing base (ab36d56) to head (348e97a).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
sql/models.py	64.28%	5 Missing ⚠️
sql/plugins/password.py	89.47%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2912      +/-   ##
==========================================
+ Coverage   78.40%   78.43%   +0.02%     
==========================================
  Files         124      125       +1     
  Lines       17628    17682      +54     
==========================================
+ Hits        13822    13869      +47     
- Misses       3806     3813       +7     

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