Update the "Ask the community for help" link in issue templates

When creating an issue in our repos, "Ask the community for help" a common option:

- https://github.com/dbt-labs/dbt-core/issues/new/choose
- https://github.com/dbt-labs/dbt-adapters/issues/new/choose
- https://github.com/dbt-labs/dbt-bigquery/issues/new/choose
- https://github.com/dbt-labs/metricflow/issues/new/choose
- etc.

If you click the "Open" link, it goes here:
- https://github.com/dbt-labs/docs.getdbt.com/discussions

But it should go here instead:
- https://discourse.getdbt.com

[Here's](https://github.com/search?q=org%3Adbt-labs+%22Ask+the+community+for+help%22&type=code) the places we want to update this:

```[tasklist]
- [ ] dbt-oss-template
- [ ] dbt-core
- [ ] dbt-adapters
- [ ] dbt-common
- [ ] dbt-bigquery
- [ ] dbt-postgres
- [ ] dbt-redshift
- [ ] dbt-snowflake
- [ ] dbt-spark
- [ ] metricflow
```