Add ordering and filtering by `package_content` in REST API packages endpoint

[tdruez]

Now that we provide some value for this, it would be useful to get the result sorted by package_content.
The ability to filter on this would be also very useful.

[JonoYang]

@tdruez I've updated the private purldb instance to have ordering and filtering on the package content field. The changes to the pypi collector is also available there as well.

[tdruez]

@JonoYang works fine, feel free to merge and deploy 👍