fix: add missing build stages and fix ordering in EE template

[NilashishC]

• Add the missing append_galaxy, prepend_builder, and append_builder stages to the execution-environment.yml.j2 template.
• Reorder all additional_build_steps blocks to follow the correct ansible-builder v3 build stage sequence: base → galaxy → builder → final.

Closes https://redhat.atlassian.net/browse/AAP-73027

[rockygeekz]

Review Summary

The fix correctly addresses the bug reported in AAP-73027, where 3 of 8 additional_build_steps stages were missing from the Jinja2 template.

What changed

1. Added 3 missing stages: append_galaxy, prepend_builder, and append_builder — all three stages that were silently dropped during EE builds.
2. Fixed stage ordering: Moved append_base to its correct position (after prepend_base, before prepend_galaxy). Previously it was rendered after prepend_galaxy, which violated the ansible-builder v3 build stage sequence.

Verification

The resulting stage order in the template is now:

prepend_base → append_base → prepend_galaxy → append_galaxy → prepend_builder → append_builder → prepend_final → append_final

This matches the ansible-builder v3 specification which defines the build stage sequence as: base → galaxy → builder → final.

Notes

• The new stage blocks follow the same conditional pattern (is defined guard + for loop) as existing stages — consistent and correct.
• The append_base block correctly preserves its special-case logic for non-official EEs (RUN $PYCMD -m pip install -U pip).
• Existing test fixtures (tests/fixtures/common/execution-environment/execution-environment.yml and tests/fixtures/project/ee_project/execution-environment.yml) don't exercise the new stages, but since those fixtures test the default non-official EE path (which only generates append_base), they remain valid. Adding a fixture that exercises all 8 stages would be a nice follow-up but isn't blocking.

LGTM — clean, minimal fix that addresses the root cause.

[rockygeekz]

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[rockygeekz]

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