Add procedure for scale-out, scale-in, server replacement chapters

[wey-gu]

The procedure should be provided in a searchable manner :)

For scale-in, the key step is to balance data remove.

https://docs.nebula-graph.io/3.1.0/synchronization-and-migration/2.balance-syntax/

note: we already have scaling chapters for the nebulagraph k8s operator.

[wey-gu]

ref on scale-in: https://discuss.nebula-graph.com.cn/t/topic/9213/2

[abby-cyber]

ref on scale-in: https://discuss.nebula-graph.com.cn/t/topic/9213/2

No commands are provided to scale a cluster. User can manually scale a cluster that is mentioned in
https://docs.nebula-graph.io/3.1.0/20.appendix/0.FAQ/#how_to_scale_out_or_scale_in_enterprise_edition_only

[wey-gu]

@abby-cyber got it, this information is the one! But it's actually not that easy for user(to seek for how to scale-in/out by searching in docs), thus I think adding a chapter may still worth it?

[abby-cyber]

Yeah, will consider it after the auto scaling commands are developed. Currently, uses can refer to FAQ for manual scaling operations.

Yeah, will consider it after the auto scaling commands are developed. Currently, uses can refer to FAQ for manual scaling operations.