fix: replace curl HEAD with GET request for proxy compatibility in RHEL recipe

[Nandu-pns]

Infrastructure agent installation fails on RHEL/CentOS 7+ systems when using HTTP proxies, with the error:

there is no newrelic infrastructure agent available for the distribution '7'.

Root Cause

The recipe's prerequisite check here uses curl -Is (HEAD request) to verify the availability of the New Relic repository:

curl -Is {{.NEW_RELIC_DOWNLOAD_URL}}infrastructure_agent/linux/yum/el/{{.DISTRO_VERSION}}/x86_64/newrelic-infra.repo

Issue

Many corporate proxies block or mishandle HEAD requests, causing this check to fail even though:

• The repository is accessible
• The CLI successfully connects to New Relic APIs (api.newrelic.com, insights-collector.newrelic.com) through the same proxy
• The HTTPS_PROXY environment variable is properly set

Solution

Changed the curl command to use a GET request instead:

curl -s -o /dev/null -w "%{http_code}" {{.NEW_RELIC_DOWNLOAD_URL}}infrastructure_agent/linux/yum/el/{{.DISTRO_VERSION}}/x86_64/newrelic-infra.repo
### Changes:

• -s = silent mode (no progress bar)
• -o /dev/null = discard response body
• -w "%{http_code}" = output only HTTP status code
• Improved regex pattern: grep -E "^2[0-9][0-9]$" for more reliable status code matching

✅ GET requests are universally supported by corporate proxies
✅ More reliable HTTP status code parsing
✅ No functional change - still validates repository availability
✅ Maintains backward compatibility with non-proxy environments

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