fixed missing today() in TimeSkill

[BeanHsiang]

Motivation and Context

the method Today() in TimeSkill.cs and today() in TimeSkill.py was missing.
Today must be an alias for Date.

Description

Add the method Today.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows SK Contribution Guidelines (https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
• The code follows the .NET coding conventions (https://learn.microsoft.com/dotnet/csharp/fundamentals/coding-style/coding-conventions) verified with dotnet format
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[MovGP0]

Instead of

    [SKFunction("Get the current date")]
    public string Today()
    {
        // Example: Sunday, 12 January, 2025
        return this.Date();
    }

You could just write

    [SKFunction("Get the current date")]
    public string Today() => Date();

[BeanHsiang]

that's better one.

[BeanHsiang]

@lemillermicrosoft
no change in any .md file, please help to pass markdown-link-check

[lemillermicrosoft]

I understand the concern of duplicate functions having some cost elsewhere. But I think that's something we should solve elsewhere as this will happen in the wild, too.