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_

まず、このcrateのREADMEをDataFusionのRustバージョン互換性ポリシーと比較し、その後、issueで参照されている既存のDataFusion CIチェックを確認します。crateのMSRVポリシーを定義してREADMEに記載し、選択した互換性レベルを強制するCIチェックを追加します。

索引モデルが issue の本文から書いたものです。