Create an MSRV policy in this crate

TLDR woudl be:
1. Define a MSRV policy (maybe copy the existing DataFusion one)
2. Implement some sort of CI check (again can copy / reuse the datafusion one if we want)
3.

🤔 interestingly we don't seem to have an MSRV policy in this crate (at least not that I could find in https://github.com/apache/datafusion-sqlparser-rs/blob/main/README.md)

We do have such a thing in DataFusion here: https://github.com/apache/datafusion?tab=readme-ov-file#rust-version-compatibility-policy

Maybe it is worth considering adding some documentation / policy in the sqlparser crate too 🤔

_Originally posted by @alamb in https://github.com/apache/datafusion-sqlparser-rs/issues/1736#issuecomment-2676808035_

首先将此 crate 的 README 与 DataFusion 的 Rust 版本兼容性策略进行比较，然后检查 issue 所引用的现有 DataFusion CI 检查。定义该 crate 的 MSRV 策略，将其记录在 README 中，并添加一个强制执行所选兼容性级别的 CI 检查。

由索引模型根据 Issue 内容生成。