Unify the HttpClient usage for avoiding anit-patterns

We found some spots that does not use HttpClient properly. Also find lack of using on the following code.
Review the following two files and use HttpClient properly.

We should use:
* HttpClientFactory with User Agent with DI
* Proper Retry-Handling using Polly if it necessary

List the Pointers:
* PowerShellFileProvisioner
* KubernetesClient

Locate the PowerShellFileProvisioner and KubernetesClient implementations and review how each currently creates or uses HttpClient. Define completion as both using HttpClientFactory with a User-Agent supplied through DI, with Polly retry handling where necessary; the issue does not name specific files or tests.

Written by the indexing model from the issue text.