Rename reports to exposures

[jtcohen6]

Describe the feature

We've had several conversations internally since #2730. While concrete, report names only a subset of the intended functionality of the new node type. We're going back to the original name, exposure, because:

• it accords with the intended superset of use cases
• it better communicates to dbt developers the why of this feature

Describe alternatives you've considered

Other names we considered:

• interfaces: good, but too vague/broad. This is a word we use often when training and talking about dbt, e.g. the way it interfaces with different databases.
• contracts: good; related but slightly different. Each dbt model might have its own contract; that one model could be exposed in different ways, however, in different downstream dashboards/reports/notebooks/applications.

Additional context

All functionality is identical. The only proposed change is replacing all instances of report(s) with exposure(s).

Future functional changes to the exposures node, out of scope here:

• Add support for tags, such that dbt ls -s tag:common_tag will return all sources, models, tests, and exposures that have common_tag

Who will this benefit?

Names are important, naming things is hard. We want to be using the best words we can when it's time to put this in front of dbt developers.

[beckjake]

Fixed in core with #2780