docs: fix a set of details spotted over time

[consideRatio]

I've collected a list of smaller details in #2041 on things to fix, and in this PR I fix point 27-31 provided for reference below.

27

I had to create a directory for my new cluster in config/clusters before letting terraform write a file to that location.

28

I saw this, but CLUSTER_NAME wasn't prefixed with $

deployer deploy-support CLUSTER_NAME

29

When configuring domain names via namecheap, it would be good to link directly to where this is done: https://ap.www.namecheap.com/Domains/DomainControlPanel/2i2c.cloud/advancedns instead of namecheap.com.

See https://infrastructure.2i2c.org/en/latest/hub-deployment-guide/deploy-support/configure-support.html#setting-dns-records

30

This command should be without create as a standalone arg

deployer cilogon-client-create create 2i2c dask-staging daskhub dask-staging.2i2c.cloud

31

Update AWS account creation docs to suggest use of email sub-addressing, like support+aws-<account name>@2i2c.org instead of creating new emails.

Related to https://github.com/2i2c-org/meta/issues/535

[pnasrat]

lgtm