Add `make print-pgtle` target for version-aware pg_tle SQL output

[jnasbyupgrade]

Summary

Add a make print-pgtle target that outputs the correct pg_tle registration SQL to stdout, using version-aware directory selection.

Motivation

When building combined pg_tle registration files (e.g., pgtle-all.sql that registers multiple extensions in dependency order), consumers currently need to know:

1. The extension name (from .control file)
2. The correct pg_tle/{version-range}/ directory for the installed pg_tle version
3. The file path within that directory

A print-pgtle target would encapsulate this logic, making combined file generation simpler:

# Current approach (consumer must know internals):
ext=$$(basename ../deps/cat_tools/*.control .control); \
echo "\\ir ../deps/cat_tools/$$(pgxntool/pgtle.sh --get-dir $$PGTLE_VERSION)/$$ext.sql"

# With print-pgtle (consumer just calls make):
$(MAKE) -C ../deps/cat_tools print-pgtle

Proposed Behavior

# Outputs the pg_tle SQL content to stdout
make print-pgtle

# With explicit version
make print-pgtle PGTLE_VERSION=1.5.2

The target would:

1. Detect pg_tle version (from PGTLE_VERSION env/var, or via pgtle.sh --get-version)
2. Select the correct version directory via pgtle.sh --get-dir
3. Output the registration SQL to stdout

This pairs well with pgxntool's existing pgtle and run-pgtle targets in base.mk.