Add link to gigs on challenge listings page on CA

[jmgasper]

REF: https://topcoder.atlassian.net/browse/PROD-4221

Describe the bug Add a Gigs link to the right of “past challenges” on the current challenge listings page that will direct user to https://www.topcoder.com/gigs

Changes

We will change:

1. The challenge listing page to add the Gigs link
2. The gigs page header

Gigs page header

We will redesign the Gigs page header to more closely match the Challenge list header.

1. Add the challenge header and tabs to the Gigs page, above the referral link
2. Change Challenges to Gig Work Opportunities
3. Show the referral section below the header

When on the Gigs page, the Gigs option in the tab list should be highlighted. The Active Challenges and Past Challenges links should go back to the challenge listing

[suppermancool]

@jmgasper done in community-app-issue-6874.patch

this PR against commit 9192e1ff926353e5ad5774f7a841f0b89552c73a (develop branch)

The GIG WORK OPPORTUNITIES text in the below screenshot is configured in Contentful you should remove it inside the Contentful dashboard with contentful item info:

{
sys.id: 3X6GfJZl3eDU0m4joSJZpN,
content_type: 'viewport'
}