Rename the feature to “Prisma relation mode” → relationMode

[Jolg42]

See details https://www.notion.so/prismaio/How-do-we-GA-the-referentialIntegrity-preview-feature-8a656fe445ae4a69ad19c5000e5c7191#72322949b0ab4343a63b6c39e4d61f19

Plan

Note: we want to ensure backward-compatibility!

• UNDO Move referentialIntegrity to the hidden feature flags, add relationMode to the active feature flags (see preview_features.rs)
• Check that referentialIntegrity is still supported as a preview feature and works as before
• Check that relationMode is supported as a preview feature and works as referentialIntegrity did before
• Rename references of referentialIntegrity=prisma/foreignKeys to relationMode
  • In prisma/prisma-engines
  • In prisma/prisma
  • In prisma/language-tools (nothing to rename)

Contributing PRs

• feat: rename 'referentialIntegrity' to 'relationMode' prisma-engines#3249
• chore: revert relationMode preview feature flag to referentialIntegrity prisma-engines#3263

[Jolg42]

@jkomyno We need to undo the preview feature flag renaming, it's not needed and makes things more complicated in the end.

[Jolg42]

Undo was done in prisma/prisma-engines#3263

And renaming was done in the tests PR #14221