Change default for /search endpoint with package filter

[ruflin]

So far when a /search?package=foo query was run, by default all versions of the package found were returned. This was in contrast to that by default only the most recent version of a package is returned. To make the API less surprising the behavior was changed that by default only the most recent package is returned.

As there might be still a need to return all packages, and additional param all=true was added. This can now be used in combination with all query params. To get the same result as before, /search?package=foo&all=true has to be run. By default all is false.

[neptunian]

@ruflin Can you update the README.md to /search's new behavior.

[jfsiii]

What about a query/filter param which takes a semver range? Perhaps versions which we have elsewhere in the API. So versions=*, versions=7.x, etc

Another option is something more explicit like include or filter (depending on the assumption). I think any of these are preferable to a Boolean param.

[ruflin]

@jfsiii I'm happy to implement some of the suggestion above. I think what I want to first fix in this PR is the surprising behaviour that when just running /search it returns 1 item per package and when adding a package filter, it returns all. I don't think this is intuitive. I would like to keep the default behaviour of only the newest. If we don't need the all at the moment, I can also remove it from the PR and just go with the query change.