[EPIC] 1.10 Deprecations + Improved Developer Experience

[QMalcolm]

There are a number of unstrict areas of core which lead to confusion unexpected behaviors when developing their projects. Additionally, some of these unstrict areas make it difficult to make changes in core to add new features. As such, we want to make these unstrict areas strict, to do so we will be deprecating the unstrictness in a number of areas for core 1.10. Deprecating these things means they will continue to work in 1.10, but will not in later versions of core.

Things to deprecate

• Deprecate user provided custom top level attributes on nodes #11336
• Deprecate custom config keys (all non dbt controlled configs should live in meta within config) #11337
• Deprecate custom top level properties in YAML files #11338
• Deprecate invalid properties under unused configuration paths #11339
• Deprecate unconstrained user space of environment variables #11340

Deprecation improvements

• deprecation warnings fire once per invocation
• in non-verbose mode a count of violations is included in the deprecation warning
• in verbose mode, each violation is listed in enough detail to find and correct the problem