Resolve revive package-comments linter errors

[austinvazquez]

Resolve the following lint errors:

Error: snapshotter/internal/integtest/stargz/fs/config/config.go:41:1: package-comments: should have a package comment (revive)
package config
^
Error: snapshotter/config/config.go:14:1: package-comments: should have a package comment (revive)
package config
^
Error: snapshotter/internal/mount/collection.go:14:1: package-comments: should have a package comment (revive)
package mount

Note: there might be more lurking

[austinvazquez]

Success criteria is these lines can be removed from .golangci.yml

    - linters:
      - revive
      text: package-comments