Add logic to disable Today button when it is not selectable

[IsabellaPap]

Tested in the demo. Works for min and max date, but also for range limit (Today will be disabled when it's out of the max range).

[github-actions]

This repository uses semantic-release to automate the process of releasing new versions. The following changelog entries would be generated for the next release. Please review them to ensure they correctly reflect the changes in this pull request.
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Changelog preview (the formatting is slightly different from the actual release):

# 19.1.0 (https://github.com/netwin/date-time-picker/compare/19.0.0...19.1.0) (2025-05-15)

### Features

    * add logic to disable Today button when it is not selectable (5a3202d (https://github.com/netwin/date-time-picker/commit/5a3202de1eba3423e539cd482ef176163b8f5af8))
    * improve scss (9d6e18c (https://github.com/netwin/date-time-picker/commit/9d6e18c304bd33925a6e1f07557d36471932c03a))

[NetWin]

lgtm, feel free to add the suggested change but not super necessary imho 👍🏼

[github-actions]

🎉 This PR is included in version 19.1.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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