Alerting: Create endpoints for exporting in provisioning file format (#58623)

This adds provisioning endpoints for downloading alert rules and alert rule groups in a 
format that is compatible with file provisioning. Each endpoint supports both json and 
yaml response types via Accept header as well as a query parameter 
download=true/false that will set Content-Disposition to recommend initiating a download 
or inline display.

This also makes some package changes to keep structs with potential to drift closer 
together. Eventually, other alerting file structs should also move into this new file 
package, but the rest require some refactoring that is out of scope for this PR.

docs/sources/alerting/set-up/provision-alerting-resources/file-provisioning/index.md

@@ -22,20 +22,20 @@ Details on how to set up the files and which fields are required for each object
 
 **Note:**
 
-Provisioning takes place during the initial set up of your Grafana system, but you can re-run it at any time using the [Grafana Alerting provisioning API](https://grafana.com/docs/grafana/latest/developers/http_api/admin/#reload-provisioning-configurations).
+Provisioning takes place during the initial set up of your Grafana system, but you can re-run it at any time using the [Grafana Admin API](https://grafana.com/docs/grafana/latest/developers/http_api/admin/#reload-provisioning-configurations).
 
 ### Provision alert rules
 
 Create or delete alert rules in your Grafana instance(s).
 
-1. Create an alert rule in Grafana.
-1. Use the [Alerting provisioning API](https://grafana.com/docs/grafana/latest/developers/http_api/alerting_provisioning/#route-get-alert-rule) to extract the alert rule.
+1. Create alert rules in Grafana.
+1. Use the [Alerting provisioning API](https://grafana.com/docs/grafana/latest/developers/http_api/alerting_provisioning/#route-get-alert-rule-export) export endpoints to download a provisioning file for your alert rules.
 1. Copy the contents into a YAML or JSON configuration file in the default provisioning directory or in your configured directory.
 
    Example configuration files can be found below.
 
 1. Ensure that your files are in the right directory on the node running the Grafana server, so that they deploy alongside your Grafana instance(s).
-1. Delete the alert rule in Grafana.
+1. Delete the alert rules in Grafana that will be provisioned.
 
    **Note:**