Expand .gitignore with common patterns (#129)

* Include rationale for keeping the top-level `.gitignore` file small.
* Expand `.gitignore` file specific to the knowledge base.

Reason for this change: my local working tree has many untracked files
that match these patterns.

Author: pietern

.gitignore

@@ -1 +1,6 @@
-.ruff_cache
+# Note: this file only excludes root level entries.
+# Subdirectories must use their own .gitignore file to make sure
+# that they are complete and can be used outside this repository.
+
+/.ruff_cache
+/.vscode

knowledge_base/.gitignore

@@ -0,0 +1,19 @@
+# Python
+__pycache__/
+dist/
+build/
+.venv/
+.pytest_cache/
+
+# Scala/SBT
+target/
+
+# Databricks
+.databricks
+
+# Editors
+.vscode/
+
+# Build artifacts
+*.jar
+*.class