Improve AWS Fargate package information

[zmoog]

What does this PR do?

This PR updates a couple of package information:

• Improve the integration description to be more specific ("collects tasks metrics" vs. "Fargate integration"), so end users will know from the integrations list what it does.
• Replace the integration screenshot with a new one, without any references to "Metricbeat".

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• Relates Migrate AWS Fargate metrics module to package #2971

Screenshots

Integrations list:

Dashboard overview:

[elasticmachine]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Start Time: 2022-04-15T17:35:45.209+0000

• Duration: 12 min 15 sec

Test stats 🧪

Test	Results
Failed	0
Passed	11
Skipped	0
Total	11

🤖 GitHub comments

To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

[ravikesarwani]

Looks good from side.