Alerting: API to create rule groups using mimirtool (#100558)

What is this feature?

Adds an API endpoint to create alert rules with mimirtool:

- POST /convert/prometheus/config/v1/rules/{NamespaceTitle} - Accepts a single rule group in a Prometheus YAML format and creates or updates a Grafana rule group from it.

The endpoint uses the conversion package from #100224.

Key parts

The API works similarly to the provisioning API. If the rule does not exist, it will be created, otherwise updated. Any rules not present in the new group will be deleted, ensuring the group is fully synchronized with the provided configuration.

Since the API works with namespace titles (folders), the handler automatically creates a folder in the root based on the provided title if it does not exist. It also requires a special header, X-Grafana-Alerting-Datasource-UID. This header specifies which datasource to use for the new rules.

If the rule group's evaluation interval is not specified, it uses the DefaultRuleEvaluationInterval from settings.

pkg/services/ngalert/api/tooling/api.json

@@ -4493,6 +4493,7 @@
    "type": "object"
   },
   "URL": {
+   "description": "The general form represented is:\n\n[scheme:][//[userinfo@]host][/]path[?query][#fragment]\n\nURLs that do not start with a slash after the scheme are interpreted as:\n\nscheme:opaque[?query][#fragment]\n\nThe Host field contains the host and port subcomponents of the URL.\nWhen the port is present, it is separated from the host with a colon.\nWhen the host is an IPv6 address, it must be enclosed in square brackets:\n\"[fe80::1]:80\". The [net.JoinHostPort] function combines a host and port\ninto a string suitable for the Host field, adding square brackets to\nthe host when necessary.\n\nNote that the Path field is stored in decoded form: /%47%6f%2f becomes /Go/.\nA consequence is that it is impossible to tell which slashes in the Path were\nslashes in the raw URL and which were %2f. This distinction is rarely important,\nbut when it is, the code should use the [URL.EscapedPath] method, which preserves\nthe original encoding of Path.\n\nThe RawPath field is an optional field which is only set when the default\nencoding of Path is different from the escaped path. See the EscapedPath method\nfor more details.\n\nURL's String method uses the EscapedPath method to obtain the path.",
    "properties": {
     "ForceQuery": {
      "type": "boolean"
@@ -4528,7 +4529,7 @@
      "$ref": "#/definitions/Userinfo"
     }
    },
-   "title": "URL is a custom URL type that allows validation at configuration load time.",
+   "title": "A URL represents a parsed URL (technically, a URI reference).",
    "type": "object"
   },
   "UpdateRuleGroupResponse": {
@@ -4931,7 +4932,6 @@
    "type": "object"
   },
   "gettableAlerts": {
-   "description": "GettableAlerts gettable alerts",
    "items": {
     "$ref": "#/definitions/gettableAlert",
     "type": "object"
@@ -5056,7 +5056,6 @@
    "type": "object"
   },
   "gettableSilences": {
-   "description": "GettableSilences gettable silences",
    "items": {
     "$ref": "#/definitions/gettableSilence",
     "type": "object"