chores: add .repo-metadata.json for google-cloud-vectorsearch (googleapis#15574)

Need to add the file before generating due to the following error:

```
LIBRARIAN_GITHUB_TOKEN=$(gh auth token) legacylibrarian generate -api=google/cloud/vectorsearch/v1 -library=google-cloud-vectorsearch -push
go: github.com/googleapis/librarian@v0.8.0 requires go >= 1.25.5; switching to go1.25.7
time=2026-02-18T01:01:32.302Z level=INFO msg="temporary working directory" dir=/tmp/librarian-1186255432
time=2026-02-18T01:01:32.302Z level=INFO msg="repo not specified, using current working directory as repo root" path=/usr/local/google/home/lingqinggan/temp/google-cloud-python
time=2026-02-18T01:01:32.302Z level=INFO msg="opening repository" dir=/usr/local/google/home/lingqinggan/temp/google-cloud-python
time=2026-02-18T01:01:39.242Z level=ERROR msg="librarian command failed" err="/usr/local/google/home/lingqinggan/temp/google-cloud-python repo must be clean"
exit status 1
```

Author: Linchin

.librarian/generator-input/packages/google-cloud-vectorsearch/.repo-metadata.json

@@ -0,0 +1,16 @@
+{
+  "api_description": "The Vector Search API provides a fully-managed, highly performant, and\nscalable vector database designed to power next-generation search,\nrecommendation, and generative AI applications. It allows you to store,\nindex, and query your data and its corresponding vector embeddings through\na simple, intuitive interface. With Vector Search, you can define custom\nschemas for your data, insert objects with associated metadata,\nautomatically generate embeddings from your data, and perform fast\napproximate nearest neighbor (ANN) searches to find semantically similar\nitems at scale.",
+  "api_id": "vectorsearch.googleapis.com",
+  "api_shortname": "vectorsearch",
+  "client_documentation": "https://cloud.google.com/python/docs/reference/google-cloud-vectorsearch/latest",
+  "default_version": "v1",
+  "distribution_name": "google-cloud-vectorsearch",
+  "issue_tracker": "https://issuetracker.google.com/issues/new?component=1899904",
+  "language": "python",
+  "library_type": "GAPIC_AUTO",
+  "name": "google-cloud-vectorsearch",
+  "name_pretty": "Vector Search API",
+  "product_documentation": "https://docs.cloud.google.com/vertex-ai/docs/vector-search-2/overview",
+  "release_level": "preview",
+  "repo": "googleapis/google-cloud-python"
+}