Added ObservedGeneration to solrcloud status

[RavinaChidambaram]

Implemented #650

Have added observed generation to the status of the solrcloud CR to track the transition of the solrcloud.

[gerlowskija]

I left one in-line question, but otherwise this LGTM. It seems to bring out status a little closer into line with best practices.

I'm ambivalent on the "lastUpdated" timestamp field that was described in the issue description. It seems like there's less strong of a precedent around that field, and it's maybe more subject to some of the "false-signal" concerns I expressed in #650. But I'm not against it - if others think it's worthwhile and are willing to add it, I'll hold off merging for a bit. But otherwise I'll add a Chart.yaml change-entry and merge this sometime in the next few days!

Thanks @RavinaChidambaram !

[gerlowskija]

[Q] Are there any edge-cases where there won't be an observedGeneration, say, immediately after creating a SolrCloud but before the operator has created any of the resources backing it?

Assuming that case exists, I guess the 'observedGeneration' would just be '0' in that case, and that's probably fine unless it'd be better to make the field an optional *int64?

[RavinaChidambaram]

Thanks for the feedback and approval. I’m currently working on considering other scenarios as well around observedGeneration, and I’ll address that within this PR. Please hold off on merging for a bit while I make these adjustments.

Also lets just address observedGeneration in this PR and then add lastTransitionTime in another PR