[DH-276] update cluster switchover doc

[shaneknapp]

update our cluster switchover docs to something relevant, recent and (mostly) complete.

at some point, i'd love for this doc to be used as a template for a "how to deploy our infra from zero to datahub".

[shaneknapp]

@ryanlovett @felder it'd be great if you could put your peepers on these changes for any feedback.

thanks!

[ryanlovett]

@shaneknapp Seems clear to me! I didn't participate in most the upgrade so I don't know if anything is missing. The cert-manager section seems accurate though, from what I recall.

Either in this PR or another, it might be good to document in a sentence or two why it can be necessary to deploy a new cluster.

[felder]

I commented and suggested edits for the specific section you asked me about. I think everything else looks reasonable, but it's hard to know for sure. I guess we can cross that bridge the next time we do a cluster rotation and refer to this doc.

[shaneknapp]

@felder let me know if the changes from 79bcd14f1f76242984e362c92bffabb9ebb66261 look good!

[shaneknapp]

@shaneknapp Seems clear to me! I didn't participate in most the upgrade so I don't know if anything is missing. The cert-manager section seems accurate though, from what I recall.

Either in this PR or another, it might be good to document in a sentence or two why it can be necessary to deploy a new cluster.

0558bb9
and
a788ff3

addressed