Draft: Update SM doc to highlight Admin account is Billable

What does this MR do and why?

Adds comment to License section of install docs for SM, to highlight that the Admin account consumes a billable seat.

Intention is for those customers who do not delve too far into our Docs, to see immediately that they will be charge for an account they may otherwise assume is free as it is installed by default.

Links to further in the docs where billable seats are explained with further link to rename or delete admin account.

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