Fix switchblade Initialize() multi-stack buildpack deletion

[tnikolova82]

Summary

Fix cf delete-buildpack failure in switchblade Initialize() when multiple
buildpacks share the same name across different stacks (cflinuxfs4 + cflinuxfs5).

Problem

When CF has both cflinuxfs4 and cflinuxfs5 stacks deployed, buildpacks like
ruby_buildpack exist once per stack. The switchblade Initialize() method
called cf delete-buildpack -f <name> without -s <stack>, causing:

Multiple buildpacks named ruby_buildpack found.
Specify a stack name by using a '-s' flag and/or lifecycle using a '-l' flag.
FAILED

This broke the create-cf-infrastructure-and-execute-integration-test-for-ruby
pipeline job — all 5 retry attempts failed identically at platform.Initialize().

Fix

In the vendored switchblade/internal/cloudfoundry/initialize.go:

• Parse the stack field from the /v3/buildpacks API response
• Iterate over all resources (one per stack) and delete each with -s <stack>
• Guard with if resource.Stack != "" to handle any-stack buildpacks (null stack)

This is a vendored fix — the same bug exists in upstream switchblade v0.9.4.

Testing

• go build ./... passes
• Docker-based switchblade tests are unaffected (different code path)
• CF integration tests should now pass with both cflinuxfs4 and cflinuxfs5

[tnikolova82]

Closing: the switchblade multi-stack fix has been merged upstream (cloudfoundry/switchblade#126) and released as v0.9.5. PR #1131 now includes the proper upstream dependency update instead of a vendored patch.