Add Payment Management System

[ChengguiSun]

Payment management system is added. Detailed information about this PR/payment system are listed as below:

• plan options: monthly plan, quartely plan, yearly plan;
• payment method include: UnionPay, WeChat Pay, Alipay;
• quota management: reguar membership and professional membership.

Type of change

Please delete options that are not relevant.

• [x] New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration:

Test Configuration:

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes

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[ChengguiSun]

I feel the "price" should be changed from a string to a number. Other than this, the PR looks good to me.

thanks for your review. I updated this.