clustergen: add all-clusters cluster

[tanner-bruce]

Adds an all-shards cluster, which contains the shard definitions for each cluster specified in the ClickhouseInstallation. This is used by our query nodes to allow scattering reads across all clusters in the CHI while respecting the shard/replica.

Please check items PR complies to:

• All commits in the PR are squashed. More info
• The PR is made into dedicated next-release branch, not into master branch¹. More info
• The PR is signed. More info

fixes #1291

[Slach]

You are ignored our recommendations about non-mental name all-shards
#1291 (comment)
could you please use another name like all-clusters?

[Slach]

Or even all-clusters-shards

[tanner-bruce]

You are ignored our recommendations about non-mental name all-shards #1291 (comment) could you please use another name like all-clusters?

Let me check what happened, I pushed the wrong code. We have it as chi-<cluster>

[tanner-bruce]

You are ignored our recommendations about non-mental name all-shards #1291 (comment) could you please use another name like all-clusters?

Fixed now. I've pushed the proper code, which changed the name to what you suggested in #1291 - chi-<cluster name>. Please let me know if you'd prefer something else. Or maybe we could make it configurable?