async registry_api & repository-stats updater

[syphar]

This refactors all usages of reqwest::blocking to async, also adding sqlx where necessary.

[syphar]

@GuillaumeGomez the test failure in the gui tests looks odd, is that flaky? How could we prevent this? rebasing deleted the test failure from the logs, and I failed to copy it here.

[syphar]

@rust-lang/docs-rs-reviewers here is another one, perhaps @GuillaumeGomez can help since I'm refactoring the repo-stats-updater ?

[GuillaumeGomez]

Looks good to me. If the tests still pass, nothing else to add I suppose. ;)