NixCon is official, 2025 organisation and location (OST in Rapperswil-Jona, Switzerland)

[infinisil]

As mentioned in #70, we had a first meeting today to start organisation of NixCon 2025. Present were @zmberber, @a-kenji, @Lassulus, @pinpox, @refroni, @Nebucatnetzer and @infinisil. While @Nebucatnetzer and @infinisil are local, the more experienced local event organisers @ners, @john-rodewald and @das-g could not attend this first meeting.

In the meeting we agreed to now work with the assumption that NixCon 2025 will be held at OST Rapperswil-Jona (Switzerland). While there are many things to figure out still, if we can make OST Rapperswil-Jona happen, let's make it happen.

Furthermore, we generally agreed that:

• NixCon should be made official and we should be delegated explicitly as organisers for this year.
• If we cannot reach consensus on important decisions, they are escalated to the Steering Committee.
• Decisions relating to sponsorships are always escalated to the Steering Committee.

This PR is still a draft because we should get confirmation from @ners, @john-rodewald and @das-g for the location and for the vital local organisation.

This needs to be approved by the SC. To implement this PR, the following also needs to happen:

• The owners of the both NixOS and NixCon GitHub organisations should be made to match (@zimbatm or @Lassulus can implement this)
• The [email protected] email should be aliased to the organisers (infra team can implement this, @infinisil has the list of emails)
• The https://github.com/nixcon/2025.nixcon.org/ repository should be created, the organisators should be given write access to it

This PR closes #22