Hide finished at time for deployments without date

What does this MR do and why?

TimeAgoTooltip defaults to now when an empty string is passed to it. Instead, we should hide the date if the deployment hasn't finished yet.

Screenshots or screen recordings

How to set up and validate locally

1. Enable the feature flag environment_details_vue
2. create a project and add the following .gitlab-ci.yaml file

stages:
    - deploy
image: alpine:latest

deploy-prod:
    stage: deploy
    script:
        - sleep 10
        - echo "deploying prod"
    environment:
        name: production
        url: postgres://example.com

deploy-staging:
    stage: deploy
    script:
        - echo "deploying staging"
    environment:
        name: staging
        url: https://example.com

1. Run the pipeline to trigger a creation of pending deployment
2. Locate your deployment on Deployments -> Environments -> Production
3. View the missing finished at date. It should appear once the deployment is successful

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.