add path ignore for markdown files (opensearch-project#2312)

To save resources and job runners, some PRs do not need to run the full test suite. For PRs and pushes with markdown changes only, the build and test workflow will be skipped. (Linter test should be okay to skipped since it will automatically run with every commit). For PRs and pushes with markdown changes along with other changes, the build and test workflow will not be skipped.

Issue Resolved:
opensearch-project#1214

Signed-off-by: abbyhu2000 <abigailhu2000@gmail.com>
Signed-off-by: Sergey V. Osipov <sipopo@yandex.ru>

.github/workflows/build_and_test_workflow.yml

@@ -7,8 +7,12 @@ name: Build and test
 on:
   push:
     branches: [ '**', '!feature/**', '!backport/**' ]
+    paths-ignore:
+      - '**/*.md'
   pull_request:
     branches: [ '**', '!feature/**' ]
+    paths-ignore:
+      - '**/*.md'
 
 env:
   TEST_BROWSER_HEADLESS: 1