Add workflow for testing with all deps (#4410)

# Add action to test with all dependencies installed

PR adds a custom action for setting up poetry that allows specifying a
cache key:
https://github.com/actions/setup-python/issues/505#issuecomment-1273013236

This makes it possible to run 2 types of unit tests: 

(1) unit tests with only core dependencies
(2) unit tests with extended dependencies (e.g., those that rely on an
optional pdf parsing library)


As part of this PR, we're moving some pdf parsing tests into the
unit-tests section and making sure that these unit tests get executed
when running with extended dependencies.

tests/data.py

@@ -0,0 +1,10 @@
+"""Module defines common test data."""
+from pathlib import Path
+
+_THIS_DIR = Path(__file__).parent
+
+_EXAMPLES_DIR = _THIS_DIR / "integration_tests" / "examples"
+
+# Paths to test PDF files
+HELLO_PDF = _EXAMPLES_DIR / "hello.pdf"
+LAYOUT_PARSER_PAPER_PDF = _EXAMPLES_DIR / "layout-parser-paper.pdf"