.Update Istio version to 1.26.6 in the OSSM 3.1.4 release.

Sail operator:

• sail operator upstream repo; release-1.0 branch (by https://github.com/istio-ecosystem/sail-operator/pull/1287 )
• sail operator midstream repo; release-3.1 branch (PR is automatically created once ^ will be merged) (https://github.com/openshift-service-mesh/sail-operator/pull/615 )
  • Finish `istio midstream repo; release-1.26 branch` step before continue! 
  • Once ^ will be merge, it is needed to generate helm charts in midstream
    • update `versions.ossm.yaml` file with newer istio values from `versions.yaml`, generate helm charts via `make gen` (see * the footer if you see error)
    • after that, make sure go.mod is referencing the latest `github.com/openshift-service-mesh/istio`
      • After the PR above^ will be merged, the job automatically update istio module, waiting
    • after that, generate `our packages` in https://github.com/openshift-service-mesh/istio-release;
      • PR: https://github.com/openshift-service-mesh/istio-release/pull/13
    • after that, update `versions.ossm.yaml` to use our generated charts and regenerate via`make gen` (see * the footer if you see error)
      • PR: https://github.com/openshift-service-mesh/sail-operator/pull/578
    • after that, create new "placeholders" images in ossm/values.yaml for new istio version, and update previous version with `shas` of already released images (if there are any from previous istio update )
      • PR: https://github.com/openshift-service-mesh/sail-operator/pull/581

Proxy:

• proxy midstream repo; release-1.26 branch (by https://github.com/openshift-service-mesh/proxy/pull/118 )

Ztunnel:

• ztunnel midstream repo; release-1.26 branch (by https://github.com/openshift-service-mesh/ztunnel/pull/12 )

Istio:

• istio midstream repo; release-1.26 branch, update sha of proxy  (by https://github.com/openshift-service-mesh/istio/pull/542 )
• istio midstream repo; release-1.26 branch sync with upstream (by https://github.com/openshift-service-mesh/istio/pull/526 )
  • do not forget to add tide/merge-method-merge label
  • after this, the `update-istio-module` job updates the istio module in sail-operator repo and creates newer PR
    • if no new PR was created, you can run the `go mod edit -replace="istio.io/istio=github.com/openshift-service-mesh/istio@release-1.26";go mod tidy` (for 1.26.z) on sail operator release-3.1 branch and create PR manually, e.g.  https://github.com/openshift-service-mesh/sail-operator/pull/623 

after that, we need to have new tags which are used in konflux.

• 1.26.6-redhat-rc tag was added to proxy/istio/ztunnel repos

after that when we will have a new build, the jenkins pipelines need to be updated as well:

• PR: https://gitlab.cee.redhat.com/istio/servicemesh-qe/jenkins-csb-declaration/-/merge_requests/811 

 
if you don't have docker cli, use `export BUILD_WITH_CONTAINER=0; make gen`, and if you see error like `license-lint: No such file or directory`, do not forget to install license-lint via `go install istio.io/tools/cmd/license-lint@v0.0.0-20250818115453-9718d40e2740` and make sure you have go bins on path `export PATH=${PATH}:`go env GOPATH`/bin`