[OAS 3.1.0] Update spec document references

[Azquelt]

Most places that the spec document talks about OpenAPI v3, it should be updated to reference version 3.1.0.

Any links in the spec document also need to be updated.

[benjamin-confino]

You can assign this one to me

[Azquelt]

Please refer to https://spec.openapis.org/oas/v3.1.0.html for the correct name of anything and link within that document where our spec needs to link to the OpenAPI spec.