Merge cli-plugin-api into cli-node

Move createCliPlugin and related types from the standalone
@backstage/cli-plugin-api package into @backstage/cli-node and
remove the now-empty package.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
Made-with: Cursor

.changeset/cli-node-add-cli-plugin.md

@@ -0,0 +1,5 @@
+---
+'@backstage/cli-node': minor
+---
+
+Added `createCliPlugin` API and related types for building Backstage CLI plugins.

.changeset/cli-use-cli-plugin-api.md

@@ -2,4 +2,4 @@
 '@backstage/cli': patch
 ---
 
-Migrated CLI plugin modules to use `createCliPlugin` from the new `@backstage/cli-plugin-api` package.
+Migrated CLI plugin modules to use `createCliPlugin` from `@backstage/cli-node`.

.changeset/create-cli-plugin-api.md

@@ -1,5 +0,0 @@
----
-'@backstage/cli-plugin-api': minor
----
-
-Added a new `@backstage/cli-plugin-api` package that provides the `createCliPlugin` API for building Backstage CLI plugins.