fix(test): enable template support in test command

[Phantal]

Summary

Enable template support in rpk connect test by explicitly passing the environment to the manager.

Problem

Templates loaded via the -t flag were not recognized during test execution (see benthos issue 287):

rpk connect test -t template.yaml test.yaml
# Error: processor type 'my_template' was not recognised

rpk connect run -t template.yaml config.yaml
# Works correctly ✓

Root Cause

RPK creates a cloned environment at startup via service.NewEnvironment(). When templates are registered, they're added to this cloned environment, not bundle.GlobalEnvironment. The test command's manager was created without explicitly passing the environment, causing it to default to bundle.GlobalEnvironment (which doesn't have templates).

Execution flow:

1. RPK clones environment → schema.Environment() (has built-in processors)
2. Templates register → schema.Environment() (now has templates too)
3. ProcessorsProvider receives → schema.Environment() (parsing works ✓)
4. Manager created with default → bundle.GlobalEnvironment (no templates ✗)

Solution

Pass the environment explicitly when creating the manager, matching the pattern used by the run command (internal/cli/common/manager.go:107).

Files changed:

• internal/cli/test/processors_provider.go - Add manager.OptSetEnvironment(p.env)
• internal/cli/test/processors_provider_test.go - Add integration test

Testing

• ✅ All existing tests pass
• ✅ New integration test verifies templates work with cloned environments
• ✅ Manual test: benthos test -t template.yaml test.yaml succeeds

Notes

• This issue only affects RPK (which uses cloned environments)
• Standalone Benthos is unaffected (uses bundle.GlobalEnvironment directly)
• The fix is minimal and follows established patterns

[CLAassistant]

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