[fix] 优化ledger 日期格式

[ramsayleung]

Description

ledger 支持多种的日期格式, 如 10-Dec-20, 2023-01-02, 或 2023/01/25, 但官方示例一般以 2023/01/25 以准，因此修改至与官方文档一致.

变更点:

1. 修改 ledger/template
2. 更新 各个 provider的 example

Motivation and Context

https://github.com/deb-sig/double-entry-generator/issues/92

Dependencies

None

Type of change

Please delete options that are not relevant.

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

How has this been tested?

make test: all tests passed

Is this change properly documented?

It's unnecessary.

Please make sure you've properly documented the changes you're making.

Don't forget to add an entry to the CHANGELOG/README if necessary (new features, breaking changes, relevant internal improvements).