Add Invocation Context Class

[peterallenwebb]

resolves #52

Housekeeping

• I am a maintainer of dbt-common

Short description

We would like to settle on a single mechanism for managing application context related to a single "invocation" of core, whether programmatically or at the command line.

Acceptance criteria

.

Suggested Tests

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Impact to Other Teams

Adapters should be given a chance to review the mechanism and provide feedback about its suitability to their work.

Will backports be required?

No.

Context

No response