Input field on manual pipeline trigger to set auth tokens

Description

As requested by customer:

BTW a sweet feature request would be an input field on manual jobs gui or even with the devops chat bot to set things such as time synced tokens.

I can definitely see the value in this, especially as it could offer a workaround to https://gitlab.com/gitlab-org/gitlab-ce/issues/13784 for many users.

Similar to https://docs.gitlab.com/ce/ci/triggers/README.html#pass-job-variables-to-a-trigger but from the UI.

Proposal

Input field that will accept a temporary auth token before starting the manual job. Could be an optional setting under pipelines.

Links / references

ZD: https://gitlab.zendesk.com/agent/tickets/75905

Documentation blurb

1. Why should someone use it; what's the underlying problem.

   To avoid using environment variables for credentials (AWS keys etc)

2. What is the solution.

   Accept auth token via input at manual job execution.

3. How does someone use this

   User creates auth token, possibly manually but most likely via API. User enters token into input field when executing a manual job.