fix: Close response to fix file descriptor leak

[jonathan-innis]

Fixes aws/karpenter-provider-aws#4296

Description

#4296 caught an issue where Karpenter was leaking file descriptors in its webhook checks. This can be observed from the following graph that shows the Karpenter container_file_descriptors metric that tracks the number of open file descriptors on a container.

The root cause of this issue is that Golang's default HTTP client opens a connection and holds that connection open when receiving a valid response from the server, which causes a file descriptor to remain open until the connection is closed (some details described here).

This issue with not closing the response body was technically introduced in the following PR: #334 (introduced in Karpenter v0.28.0) but did not become an issue until v0.29.1 since the response returned by the server used in v0.28.0-v0.29.0 did not send a response body. Adding a response body to the response sent from the server called out to in these version also results in a file descriptor leak.

This change closes the response body and and ensures that the response body is read so that the http client can re-use the same connection from the connection pool instead of having to create another one. The file descriptor leak can seen to be resolved through the container_file_descriptors metric now:

How was this change tested?

make presubmit

• Deployed and viewed prometheus metrics
• Confirmation in the issue from the user who reported it

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[coveralls]

Pull Request Test Coverage Report for Build 5602477955

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.1%) to 81.29%

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Totals
Change from base Build 5600975159:	-0.1%
Covered Lines:	6904
Relevant Lines:	8493

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💛 - Coveralls