MSSQL MCP DescribeTable tool only works with SQL Server 2017 (14.x) and later

MSSQL MCP DescribeTable tool fails with error

```json
{"success":false,"error":"Incorrect syntax near \u0027(\u0027."}
```

when used with an old SQL server version (or, in my case, a database with a compatibility level lower than 140).

This happens because the [STRING_AGG](https://learn.microsoft.com/en-us/sql/t-sql/functions/string-agg-transact-sql?view=sql-server-ver17) SQL function, which is used in the implementation of `DescribeTable`, was only introduced in SQL Server 2017 (14.x).

There are other approaches that accomplish the same thing and also work with older version of SQL server, but probably it's not worth it to introduce such a workaround for such old versions.

I was able to work around this issue by increasing the compatibility level of my local database:

```sql
alter database current set compatibility_level = 160;
```

Start at the MSSQL MCP DescribeTable implementation and inspect the query using STRING_AGG. Reproduce the failure against a database with compatibility level below 140, then determine whether the tool should support that level and verify the chosen behavior against an older SQL Server compatibility setting.

Scritto dal modello di indicizzazione a partire dal testo della issue.