Update community meeting frequency to fortnightly

[jmhbnz]

As discussed at our recent community meeting we have run a brief survey to get consensus on how often the community would like to meet.

The survey results are now in and the community would prefer to move to fortnightly meetings.

[serathius]

Will update the meeting as soon this is merged. Thanks for making sure documentation is up to date!

[serathius]

https://github.com/etcd-io/etcd#community-meetings needs a similar update.

[jmhbnz]

https://github.com/etcd-io/etcd#community-meetings needs a similar update.

Good catch, raised etcd-io/etcd#16189.

[ahrtr]

@spzala @ptabor @mitake

[spzala]

Related PR for the etcd repo - etcd-io/etcd#16189