Add blueprint for a Global Configuration object

[ocket8888]

Currently, we use a ton of "global" Parameters to configure large-scale settings for ATC instances. Not only are many of these undocumented, but they are by nature prone to human error. Any user (with the right Permissions) could accidentally delete the Parameter, or associate it with the wrong Profile (or no Profile at all which is only sometimes a problem), or make a value that may seem correct and they are given no warning or error by either TP or the TO API but the value is invalid or unusable. And of course in nearly every case it's possible that more than one Parameter that something would use exists, because multiple Parameters by the same Name and with the same Config File can exist with differing Values. In these cases, the value that's actually used any given time a component checks the Parameter is an implementation detail of PostgreSQL (at best).

Naturally, what "global" means is also highly nebulous. There are some instances where a component checks for a Parameter with some given Name, with no other criteria, so any Parameter with that name assigned to any Profile of any Profile Type in any CDN - or not assigned to any Profile(s) at all - with that Name will be considered "global" under some circumstances. Sometimes a check is made for a Parameter with a specific Name assigned to a Profile with the Name "GLOBAL" (which may or may not exist, can be in any CDN, have any Profile Type, and be assigned to any server(s) and/or Delivery Service(s)). Sometimes a check is made for some Parameter with a specific name and the Config File value "global". Sometimes something will look for a Parameter in the CRConfig.json Config File. And there are checks for any combination of these restrictions.

Instead, it would be more deterministic, easier to use, more visible, and enable validation of settings if there were just a single "Global Configuration". Furthermore, components would no longer need to handle the case where a setting does not exist.

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Which Traffic Control components are affected by this PR?

None.

What is the best way to verify this PR?

Read the blueprint.

PR submission checklist

• [x] This PR doesn't need tests
• [x] This PR doesn't need documentation
• [x] This PR doesn't need a CHANGELOG.md entry
• [x] This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY