Add EEX holiday calendar for futures

[ksenia1997]

I am requesting the addition of the EEX (European Energy Exchange) holiday calendar for futures to the exchange_calendars project.

The EEX holiday calendar provides important information regarding trading holidays and non-trading days specific to EEX futures, and its inclusion would greatly benefit users who rely on this calendar for trading and scheduling purposes.

Details:

• Calendar Source: Link to the EEX holiday calendar PDF
• Importance: EEX is a significant exchange for energy futures trading in Europe, and having its holiday calendar available in exchange_calendars would enhance the utility of the project for users in the energy trading domain.

Thank you for considering this request.

[maread99]

Added by #385 / #386.

Thanks for raising this @ksenia1997, and thanks to @romanzdk for implementing.