feat(docs): Add product neutral guides (#32256)

Author: bshaffer

help/.gitignore

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+doc/*
+.yardoc

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+# Client Configuration
+
+The Google Cloud Ruby Client Libraries allow you to configure client behavior via keyword arguments passed to the client constructor (or `configure` blocks).
+
+## 1. Customizing the API Endpoint
+
+You can modify the API endpoint to connect to a specific Google Cloud region or to a private endpoint.
+
+### Connecting to a Regional Endpoint
+
+```ruby
+require "google/cloud/pubsub"
+
+# Connect explicitly to the us-east1 region
+pubsub = Google::Cloud::Pubsub.new(
+  endpoint: "us-east1-pubsub.googleapis.com:443"
+)
+```
+
+## 2. Authenticating
+
+## See [Authentication](https://docs.cloud.google.com/ruby/docs/reference/help/authentication) for a comprehensive guide.
+
+## 3. Logging
+
+## See [Troubleshooting](https://docs.cloud.google.com/ruby/docs/reference/help/troubleshooting) for a comprehensive guide.
+
+## 4. Configuring a Proxy
+
+The configuration method depends on whether the client uses gRPC (most clients) or REST (e.g., Storage, BigQuery partial).
+
+### Proxy with gRPC
+
+The Ruby gRPC layer respects standard environment variables. You generally do not configure this in the Ruby code itself.
+
+Set the following environment variables in your shell or Docker container:
+
+```
+export http_proxy="http://proxy.example.com:3128"
+export https_proxy="http://proxy.example.com:3128"
+```
+
+**Handling Self-Signed Certificates (gRPC):** If your proxy uses a self-signed certificate, point gRPC to the CA bundle:
+
+```
+export GRPC_DEFAULT_SSL_ROOTS_FILE_PATH="/path/to/roots.pem"
+```
+
+### Proxy with REST (e.g., Google::Cloud::Storage)
+
+The underlying HTTP libraries in Ruby (often `Faraday` or `httpclient`) also respect the standard `http_proxy` environment variables automatically.
+
+However, if you must configure it in code (specifically for `Google::Cloud::Storage`), you can pass connection options:
+
+```ruby
+require "google/cloud/storage"
+
+storage = Google::Cloud::Storage.new(
+  connection_options: {
+    proxy: "http://user:password@proxy.example.com"
+  }
+)
+```
+
+## 5. Configuring Retries and Timeouts
+
+Ruby uses **Seconds** (Float/Integer) for time values.
+
+### Per-Call Configuration (Recommended)
+
+You can override settings for specific calls using keyword arguments (`retry_policy` and `timeout`).
+
+```ruby
+require "google/cloud/secret_manager"
+
+# Instantiate the client
+# Note: secret_manager_service gives access to the V1 GAPIC client
+client = Google::Cloud::SecretManager.secret_manager_service
+
+# Prepare the request
+parent = "projects/my-project"
+
+# Advanced Retry Configuration
+# Note: Time values are in SECONDS
+retry_policy = {
+  initial_delay: 0.5,    # Start with 0.5s wait
+  max_delay: 5.0,        # Cap wait at 5s
+  multiplier: 2.0,       # Double the wait each time
+  retry_codes: [14]      # Retry on specific gRPC error codes (e.g., UNAVAILABLE)
+}
+
+# Make the call
+request = { parent: parent }
+options = Gapic::CallOptions.new(
+  retry_policy: retry_policy,
+  timeout: 15.0
+)
+client.list_secrets request, options
+```
+
+### Available `retry_policy` Keys
+
+| Key | Type | Description |
+| ----- | ----- | ----- |
+| `initial_delay` | Float | Wait time before the first retry (in **seconds**). |
+| `max_delay` | Float | The maximum wait time between any two retries (in **seconds**). |
+| `multiplier` | Float | Multiplier applied to the delay after each failure. |
+| `retry_codes` | Array | List of gRPC error codes (integers) that should trigger a retry. |
+
+### Global Client Configuration
+
+You can configure defaults globally when initializing the low-level GAPIC client, though per-call is preferred for specific logic.
+
+```ruby
+require "google/cloud/pubsub"
+
+# Create a client with a custom timeout for all requests
+pubsub = Google::Cloud::Pubsub.new(
+  timeout: 10 # Default 10 seconds for all operations
+)
+```
+
+## 6. Other Common Configuration Options
+
+The following options can be passed to the constructor of generated clients (e.g., `Google::Cloud::Pubsub`, `Google::Cloud::Spanner`, `Google::Cloud::Storage`).
+
+| Option Key | Type | Description |
+| ----- | ----- | ----- |
+| `credentials` | String / Hash | Path to the JSON keyfile or the JSON object itself. |
+| `endpoint` | String | The address of the API remote host. Used for Regional Endpoints (e.g., `us-central1-pubsub.googleapis.com:443`). |
+| `lib_name` / `lib_version` | String | Used to append identification to the `x-goog-api-client` header for tracing/debugging. |
+| `timeout` | Numeric | The default timeout (in **seconds**) for requests. |
+| `retries` | Integer | Number of retries for the underlying HTTP/gRPC connection (distinct from logic retries). |
+| `project_id` | String | Explicitly sets the project ID, overriding environment variables. |
+| `universe_domain` | String | Overrides the default service domain (defaults to `googleapis.com`) for Cloud Universe support. |