Clarify Site Id vs Site Name in configuration

[mcoles]

We use "site name" in the configuration yaml file when it should really be "Site id"--the url-friendly version of the site name, much in the same way that repository URLs are the url-friendly version of the workbook/view name. We should clarify in the vizalerts.yaml and any other place that we mean "Site id" instead, as it's caused at least one person confusion:

see: https://community.tableau.com/docs/DOC-11032