Pin Opensearch versions for local instance

Why these changes are being introduced:

We formerly documented and used the tag ':latest' for standing up a local
Opensearch instance, but this has the potential to pull a newer version than
we currently have in AWS.

How this addresses that need:
* Pins references in README and Docker Compose YAML to version 2
* Will require updates when we eventually migrate to version 3

Side effects of this change:
* Build Opensearch 2.x locally for testing and development

Relevant ticket(s):
* None

Author: ghukill

README.md

@@ -21,7 +21,7 @@ TIMDEX! Index Manager (TIM) is a Python CLI application for managing TIMDEX indi
 ``` bash
 docker run -p 9200:9200 -p 9600:9600 -e "discovery.type=single-node" \
 -e "plugins.security.disabled=true" \
-opensearchproject/opensearch:2.11.1
+opensearchproject/opensearch:2
 ```
 
 2. To confirm the instance is up, run `pipenv run tim -u localhost ping` or visit http://localhost:9200/. This should produce a log that looks like the following:
@@ -54,8 +54,8 @@ OPENSEARCH_INITIAL_ADMIN_PASSWORD=SuperSecret42!
 1. Run the following command:
 
 ```shell
-docker pull opensearchproject/opensearch:latest
-docker pull opensearchproject/opensearch-dashboards:latest
+docker pull opensearchproject/opensearch:2
+docker pull opensearchproject/opensearch-dashboards:2
 docker compose up
 ```
 

compose.yaml

@@ -1,6 +1,6 @@
 services:
   opensearch:
-    image: opensearchproject/opensearch:latest
+    image: opensearchproject/opensearch:2
     ports:
       - "9200:9200"
       - "9600:9600"
@@ -15,7 +15,7 @@ services:
     networks:
       - opensearch-local-net
   dashboard:
-    image: opensearchproject/opensearch-dashboards:latest
+    image: opensearchproject/opensearch-dashboards:2
     ports:
       - "5601:5601"
     environment: