refactor: Rename RuleOrigin to Linter

"origin" was accurate since ruff rules are currently always modeled
after one origin (except the Ruff-specific rules).

Since we however want to introduce a many-to-many mapping between codes
and rules, the term "origin" no longer makes much sense. Rules usually
don't have multiple origins but one linter implements a rule first and
then others implement it later (often inspired from another linter).
But we don't actually care much about where a rule originates from when
mapping multiple rule codes to one rule implementation, so renaming
RuleOrigin to Linter is less confusing with the many-to-many system.

.github/workflows/ci.yaml

@@ -94,7 +94,7 @@ jobs:
           profile: minimal
           override: true
       - uses: Swatinem/rust-cache@v1
-      - run: ./scripts/add_rule.py --name DoTheThing --code PLC999 --origin pylint
+      - run: ./scripts/add_rule.py --name DoTheThing --code PLC999 --linter pylint
       - run: cargo check
       - run: ./scripts/add_plugin.py test --url https://pypi.org/project/-test/0.1.0/
       - run: cargo check