Add REST embeddings & system_instruction sample (google-gemini#429)

* Add REST embeddings sample

* Add system_instruction shell script as well

* Update region tags

Author: shilpakancharla

samples/rest/embeddings.sh

@@ -0,0 +1,32 @@
+set -eu
+
+echo "[START embed_content]"
+# [START embed_content]
+curl "https://generativelanguage.googleapis.com/v1beta/models/text-embedding-004:embedContent?key=$GOOGLE_API_KEY" \
+-H 'Content-Type: application/json' \
+-d '{"model": "models/text-embedding-004",
+    "content": {
+    "parts":[{
+      "text": "Hello world"}]}, }' 2> /dev/null | head
+# [END embed_content]
+
+echo "[START batch_embed_contents]"
+# [START batch_embed_contents]
+curl "https://generativelanguage.googleapis.com/v1beta/models/text-embedding-004:batchEmbedContents?key=$GOOGLE_API_KEY" \
+-H 'Content-Type: application/json' \
+-d '{"requests": [{
+      "model": "models/text-embedding-004",
+      "content": {
+      "parts":[{
+        "text": "What is the meaning of life?"}]}, },
+      {
+      "model": "models/text-embedding-004",
+      "content": {
+      "parts":[{
+        "text": "How much wood would a woodchuck chuck?"}]}, },
+      {
+      "model": "models/text-embedding-004",
+      "content": {
+      "parts":[{
+        "text": "How does the brain work?"}]}, }, ]}' 2> /dev/null | grep -C 5 values
+# [END batch_embed_contents]

samples/rest/system_instruction.sh

@@ -0,0 +1,13 @@
+set -eu
+
+echo "[START system_instruction]"
+# [START system_instruction]
+curl "https://generativelanguage.googleapis.com/v1beta/models/gemini-1.5-pro-latest:generateContent?key=$GOOGLE_API_KEY" \
+-H 'Content-Type: application/json' \
+-d '{ "system_instruction": {
+    "parts":
+      { "text": "You are a cat. Your name is Neko."}},
+    "contents": {
+      "parts": {
+        "text": "Hello there"}}}'
+# [END system_instruction]