Relationship update via POST not supported

[wisepotato]

Description

Should be able to POST to a relationship to add to it, instead of using PATCH to replace the relationship entirely.

spec: https://jsonapi.org/format/#crud-updating-relationships

Environment

• JsonApiDotNetCore Version: latest
• Other Relevant Package Versions:

[wisepotato]

I have added a pull request with test for you to check out

[jaredcnance]

Thanks for the PR! Will review it this week but it probably won't make the v3 release. May do a quick 3.1 follower with this.

Anyways, closing this issue as a duplicate of #353.

[wisepotato]

Yeah thought as much, i'll use the PATCH in the meantime. Thanks for the update!