pluto: Single client: reqwest::Client declaration

[etungsten]

Issue #, if available: #389

Description of changes:
Removes redundant declarations of reqwest::Client and let each
get_x_setting function borrow a single instance of reqwest::Client.

Testing:
Launch Thar instance and verified that all settings were still being generated correctly:

kubelet-env:

bash-5.0# cat /etc/kubernetes/kubelet/env        
NODE_IP=192.168.33.239
NODE_LABELS=testLabel=foo,testLabel2=bar
NODE_TAINTS=dedicated=experimental:PreferNoSchedule,special=true:PreferNoSchedule
POD_INFRA_CONTAINER_IMAGE=602401143452.dkr.ecr.us-west-2.amazonaws.com/eks/pause-amd64:3.1

MaxPods:

bash-5.0# cat /etc/kubernetes/kubelet/config     
...
MaxPods: 29

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[etungsten]

Addresses @tjkirch 's comment.
Edit: Didn't actually add my changes. Added in the push below

[zmrow]

🌵