Unify discussion channels

[kordano]

Currently, we have too many channels for interacting with the community and sometimes it's difficult to keep up.
I propose that we would have github for

• bug reports
• feature requests
• discussions that we would like to preserve

For direct messages I would favor slack over Discord and close the latter one. And if there are longer discussions on slack I would direct them here instead.

[TimoKramer]

We could have a public meeting open for the community on slack instead of Discord. Since it is a paid version for now slack has the feature called 'huddle' that we can use for this.

[TimoKramer]

We should remove the Discord-Link from the website datahike.io

[TimoKramer]

and from the README