plugin.json schema updates (#27029)

* added $schema field support in plugin.schema.json

More details can be found in https://github.com/grafana/plugin-validator/issues/1

* Others category in plugin.json, minimum 1 keyword 

* Allow others as a category if the plugin doesn't fall into appropriate category. Refer https://github.com/grafana/plugin-validator/issues/3 for more details
* Mandate minimum one keyword for better discovery in plugin repository.

* Dropped enum from plugin.json $schema

docs/sources/developers/plugins/plugin.schema.json

@@ -7,6 +7,10 @@
   "required": ["type", "name", "id", "info", "dependencies"],
   "additionalProperties": false,
   "properties": {
+    "$schema": {
+        "type": "string",
+        "description": "Schema definition for the plugin.json file"
+    },
     "id": {
       "type": "string",
       "description": "Unique name of the plugin. If the plugin is published on grafana.com, then the plugin id has to follow the naming conventions.",
@@ -23,8 +27,8 @@
     },
     "category": {
       "type": "string",
-      "description": "Plugin category used on the Add data source page. Possible values are: `tsdb`, `logging`, `cloud`, `tracing`, and `sql`.",
-      "enum": ["tsdb", "logging", "cloud", "tracing", "sql"]
+      "description": "Plugin category used on the Add data source page. Possible values are: `tsdb`, `logging`, `cloud`, `tracing`, `sql`, `enterprise` and `other`.",
+      "enum": ["tsdb", "logging", "cloud", "tracing", "sql", "enterprise", "other"]
     },
     "annotations": {
       "type": "boolean",
@@ -146,7 +150,7 @@
     "info": {
       "type": "object",
       "description": "Metadata for the plugin. Some fields are used on the plugins page in Grafana and others on grafana.com if the plugin is published.",
-      "required": ["logos", "version", "updated"],
+      "required": ["logos", "version", "updated", "keywords"],
       "additionalProperties": false,
       "properties": {
         "author": {
@@ -177,6 +181,7 @@
         "keywords": {
           "type": "array",
           "description": "Array of plugin keywords. Used for search on grafana.com.",
+          "minItems": 1,
           "items": {
             "type": "string"
           }