[Feature] Exposures: stricter validation for `name`, support custom `label`

[jtcohen6]

Is this your first time submitting a feature request?

• [X] I have read the expectations for open source contributors
• [X] I have searched the existing issues, and I could not find an existing issue for this feature
• [X] I am requesting a straightforward extension of existing dbt functionality, rather than a Big Idea better suited to a discussion

Describe the feature

Currently, it's possible to define an exposure like:

exposures:
  - name: My Cool Exposure
     ...

A surprising number of things will keep working:

$ dbt list --resource-type exposure
exposure:my_project.My Cool Exposure

The problem is that it's not guaranteed to work everywhere. In particular, the dbt-docs site DAG selection does not handle exposure names with spaces (https://github.com/dbt-labs/dbt-core/issues/2970).

Rather than fix it everywhere, I'd prefer to adopt the same approach we'll be taking for metrics (https://github.com/dbt-labs/dbt-core/issues/5456):

• Have stricter parse-time validation on the name property of exposures: snake-case, alphanumeric characters, maybe periods (since this is supported for models)
• Support a label property that can be used in external metadata, and contain whatever characters the heart desires

exposures:
  - name: my_cool_exposures
    label: My Cool Exposure
     ...

Describe alternatives you've considered

• Continue to support whatever exposure names users want, and they only find out much later
• Add tons of strict validation without supporting a custom human-friendly label

I don't like either very much!

Who will this benefit?

• Users of exposures
• Programmatic integrations with exposures (e.g. https://hightouch.com/blog/introducing-dbt-exposures-for-hightouch/)

Are you interested in contributing this feature?

Perhaps :)

Anything else?

No response