feat(source/template): add fqdn-target-template to pod/service/node and consolidate duplicate template helpers

[ivankatliarchuk]

What does it do ?

• pod, service, and node sources supported --fqdn-template and --target-template but not --fqdn-target-template (host:target pairs), unlike gloo, traefik, f5, and unstructured
• EndpointsForHostsAndTargets lived in source/unstructured.go despite being a pure endpoint utility with no source-specific logic

Motivation

It could be refactored further, let's say this is going to be to-path refactor. And this is a first step.

• The endpointsFromXxxFQDNTargetTemplate pattern (split host:target pairs, validate, build endpoints) was copy-pasted verbatim across 8 source files with only the log-message resource kind differin
• Consolidate 13 duplicated helper methods into template.Engine: add ApplyFQDNTargetTemplate(existing, obj) and ApplyTemplate(existing, obj) as canonical engine methods replacing 8 × endpointsFromXxxFQDNTargetTemplate and 5 × endpointsFromXxxTemplate across gloo, traefik, f5-virtualserver, f5-transportserver, unstructured, service, pod, and node - each call site shrinks from ~10 lines with a lambda closure to a single engine method call

More

• Yes, this PR title follows Conventional Commits
• Yes, I added unit tests
• Yes, I updated end user documentation accordingly

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[coveralls]

Coverage Report for CI Build 27505670507

Warning

Build has drifted: This PR's base is out of sync with its target branch, so coverage data may include unrelated changes.
Quick fix: rebase this PR. Learn more →

Coverage decreased (-0.2%) to 81.196%

Details

• Coverage decreased (-0.2%) from the base build.
• Patch coverage: No coverable lines changed in this PR.
• 196 coverage regressions across 8 files.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

196 previously-covered lines in 8 files lost coverage.

File	Lines Losing Coverage	Coverage
traefik_proxy.go	88	67.68%
template/engine.go	49	66.04%
service.go	22	94.97%
gloo_proxy.go	18	74.5%
node.go	7	92.06%
pod.go	4	96.65%
f5_transportserver.go	4	79.46%
f5_virtualserver.go	4	80.17%

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Coverage Stats

Relevant Lines:	20974
Covered Lines:	17030
Line Coverage:	81.2%
Coverage Strength:	1484.44 hits per line

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💛 - Coveralls