Add Pester (used in jenkinsci/docker* repositories)

[lemeurherve]

What feature do you want to see added?

It would be nice to add https://github.com/pester/Pester (version 5.3.3) to Windows provisioning so we won't need to install it before each docker images testing.

Concerns:

• https://github.com/jenkinsci/docker/blob/4ffcdd648ae8939aa657bd17cf65836006775c22/make.ps1#L121-L131
• https://github.com/jenkinsci/docker-agent/blob/3c4d2b17bae239f3f00fe9698bb36a04ac512f34/build.ps1#L178-L189
• https://github.com/jenkinsci/docker-ssh-agent/blob/d1bfd814232ea509e555d50c55c972a5f24fb941/build.ps1#L188-L199

Upstream changes

No response