Send project IDs as integers for release endpoints #3066
Description
Self hosted versions (besides the most recent ones) only can take project IDs at the release endpoints when they are serialized as JSON integers, not as strings, as they are affected by a bug which was only fixed in getsentry/sentry#105159.
Although SaaS and new self-hosted versions will now accept project IDs when serialized as strings, we should serialize them as integers, instead, to ensure compatibility with older self-hosted versions.