chore: Add YUM repo file and upload instructions. (#2491)

Author: tippmar-nr

build/Linux/yum/README.md

@@ -0,0 +1,8 @@
+This folder contains the YUM repo definition file for the .NET agent and was manually uploaded to https://download.newrelic.com/dot_net_agent/yum. 
+
+If changes to this file are needed, use the AWS CLI to upload to the S3 bucket:
+```
+$env:AWS_ACCESS_KEY_ID="access_key_for_s3_bucket"
+$env:AWS_SECRET_ACCESS_KEY="secret_access_key_for_s3_bucket"
+ aws s3 cp ./newrelic-dotnet-agent.repo s3://<bucket_name>/dot_net_agent/yum
+ ```

build/Linux/yum/newrelic-dotnet-agent.repo

@@ -0,0 +1,6 @@
+[newrelic-dotnet-agent-repo]
+name=New Relic .NET agent for Linux
+baseurl=https://yum.newrelic.com/pub/newrelic/el7/$basearch
+enabled=1
+gpgcheck=1
+gpgkey=https://download.newrelic.com/548C16BF.gpg