test(client): add relationMode datasource property tests for all databases

[Jolg42]

Related: #10806

RELATION_MODE=foreignKeys pnpm run test:functional:code --relation-mode-tests-only
RELATION_MODE=prisma pnpm run test:functional:code --relation-mode-tests-only
pnpm run test:functional:code --relation-mode-tests-only

# Or only one relation type by providing the file name:
pnpm run test:functional:code --relation-mode-tests-only relationMode/tests_m-to-n.ts

How to run - Previously (early commit)

RELATION_MODE=foreignKeys pnpm run test:functional:code relationMode
RELATION_MODE=prisma pnpm run test:functional:code relationMode
pnpm run test:functional:code relationMode

# Or only one relation type by providing the file name:
pnpm run test:functional:code relationMode/tests_m-to-n.ts

and before

RI=foreignKeys pnpm run test:functional:code referential-integrity
RI=prisma pnpm run test:functional:code referential-integrity
pnpm run test:functional:code referential-integrity

# Or only one relation type by providing the file name:
pnpm run test:functional:code referential-integrity/tests_m-to-n.ts

Internal Notion pages

• Project
• Findings

[jkomyno]

Note: referentialIntegrity: "prisma" already shows differences w.r.t. referentialIntegrity: "foreignKeys":

• 1:1 mandatory (explicit) › [create] child with non existing parent should throw doesn't throw a foreign key constraint violation error
• slightly different logs (e.g., mentioning the userId column rather than id)

[Jolg42]

Note: we need to await expect(...).rejects/resolves. (see linting errors)