Update features.yml with more info for package

REVIEW APP: https://trizzi-master-patch-79429.about.gitlab-review.app/features/index.html#package

Why is this change being made?

JFrog recently updated their marketing material to compare their offering to GitLab, Harbor and Docker. We discussed the comparison in slack here and thought it would be valuable to ensure that our features page includes these various talking points.

This MR adds:

• Use search to find and identify Docker images (Image search)
• Lower the cost of storage for the GitLab Container Registry by running garbage collection (Garbage collection)
• Support the most common package manager formats (Supported package types)
• Host multiple registries (Multiple registiries)
• Leverage virtual package repositories to simplify package management workflows. (Virtual repositories)
• Proxy remote package registries for safer, more reliable builds. (Proxy remote registries)

We already had:

• High availability
• Replication
• Authentication
• Permissions
• Storage
• Image security scanning

This MR does not add, since I have not heard any users/customers ask for these:

• User plugins
• Custom metadata
• Advanced querying

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Does this MR meet the acceptance criteria?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what