Add setting postConfigureTask

[snehara99]

This is to revert the reversion of #4566. This is @Francois-Le's contribution and they need to agree to our CLA before merging this feature is possible. The original PR was reverted because this agreement wasn't given.

[snehara99]

@Francois-Le please read the following Contributor License Agreement(CLA). If you agree with the CLA, please reply with the following information.

@microsoft-github-policy-service agree [company="{your company}"]

Options:

• (default - no company specified) I have sole ownership of intellectual property rights to my Submissions and I am not making Submissions in the course of work for my employer.

@microsoft-github-policy-service agree

• (when company given) I am making Submissions in the course of work for my employer (or my employer has intellectual property rights in my Submissions by contract or applicable law). I have permission from my employer to make Submissions and enter into this Agreement on behalf of my employer. By signing below, the defined term “You” includes me and my employer.

@microsoft-github-policy-service agree company="Microsoft"

[Francois-Le]

@microsoft-github-policy-service agree