Speedup Invoke-WebRequests by disabling progress indicator.

[sgtwilko]

Description

Normal ProgressPreference really slows down invoke-webrequest as it tries to update the screen for bytes received.
By setting ProgressPreference to silentlyContinue it doesn't try to update the screen and speeds up the downloads.
See https://stackoverflow.com/a/43477248/2641196

Motivation and Context

This change make a reasonable difference to the speed of accessing Jira systems with large numbers of fields, or for methods that make large number of calls.
This improves, but does not entirely resolve #362

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• I have added Pester Tests that describe what my changes should do.
• I have updated the documentation accordingly.

[lipkau]

I don't see a problem with the code - but with the behavior, it introduces.

currently, the module respects the user's value for $ProgressPreference.
meaning: the user can have the behavior introduced with this PR by setting

$ProgressPreference = "SilentlyContinue"

in his script/console.

I need more opinions on this.
cc @brianbunke , @alexsuslin , @replicaJunction , @Dejulia489 , @beaudryj , @FriedrichWeinmann , @KevinMarquette

[brianbunke]

Seems fine; the progress bar is pretty notorious at this point for its performance impact. I respect the argument for taking a choice away from the user, but I think improving performance by ~20% (per the linked issue) is understandable.

Thanks @sgtwilko!

[sgtwilko]

@lipkau Hiya, I upgraded recently and my change doesn't seem to be in the latest version.
Did I do something wrong when submitting this PR?