Refactor: Use GHA native dispatch for registry metadata build kickoff

[guineveresaenger]

This pull request removes the dependency on pulumictl for the bridged provider registry docs dispatch.

Before this change

Currently, the Create Docs Build step in the Release Workflow calls into a Pulumictl command that triggers the Publish Provider Update Workflow, building metadata, in pulumi/registry.

publish.yml(provider) -> pulumictl(bespoke command) -> publish-provider-update(registry)

After this change

Use peter-evans/repository-dispatch@v3 to dispatch the resource-provider event that already exists on the registry publish-provider-update Workflow, removing the need for pulumictl.

The registry's Action has a few fields we do not use. See example run. Filed pulumi/registry#4671 to track. The repository dispatch payload therefore only contains:

"project": "${{ github.repository }}", - this is somewhat unnecessary but makes for a safe refactor without having to change the registry workflow file
"shortname": "#{{ .Config.provider }}#", - Just the provider name without `pulumi-` prefix
"ref": "${{ github.ref_name }}" - This is the tag name of the release.

Note: This pull request changes bridged providers only since we are currently working on unifying templating for native and bridged providers. I'm happy to add native provider changes to this effect if reviewers would prefer.

[iwahbe]

This looks extremely safe to me. Let's make sure that we have a test run to show before we merge for the whole fleet.

[guineveresaenger]

Needs better JSON formatting. Be back with those changes.

[guineveresaenger]

Update: This ran correctly against pulumi-dbtcloud:
Registry build here: https://github.com/pulumi/registry/actions/runs/9455770701/job/26046268147

[danielrbradley]

Nice simplification! There's a possibility our PRs might conflict as we're editing the same files ... but it's a different area edited so might be fine.