Updating changie.yaml to add contributors and PR links

[leahwicz]

resolves #219
Goes hand in hand with dbt-labs/dbt-postgres#134

Problem

This updates changie so that we are able to display PR links. It also adds the ability to generate a contributor list when there are external contributors. Basically it matches what the Snowflake and Core repos are doing for changelog.

Solution

Copied over the Snowflake .changie file and tweaked it with the correct repo name.

Tested Locally

1. Created some fake unreleased change files
2. Populated a fake Core team env var: export CHANGIE_CORE_TEAM=dbeatty10
3. Ran: changie batch 1.4.1
4. This file was generated with a PR link as well as a contributor list that excludes dbeatty10 but includes other handles from existing unreleased changes:
   1.4.1.md

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development, and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc.) or this PR has already received feedback and approval from Product or DX

[cla-bot]

Thank you for your pull request and welcome to our community. We could not parse the GitHub identity of the following contributors: Leah Antkiewicz.
This is most likely caused by a git client misconfiguration; please make sure to:

1. check if your git client is configured with an email to sign commits git config --list | grep email
2. If not, set it up using git config --global user.email [email protected]
3. Make sure that the git commit email is configured in your GitHub account settings, see https://github.com/settings/emails