feat(chains): expose storage.oci.encoding-format in CRD

[infernus01]

Changes

tektoncd/chains#1691 added a new storage.oci.encoding-format config
key that controls how Chains serializes OCI signatures and attestations:
dsse (default, tag-based) or sigstore-bundle (OCI 1.1 Referrers API).

This PR exposes that key through the operator so it can be set via the
TektonChain and TektonConfig CRDs.

What was added

• ChainProperties.StorageOCIEncodingFormat (tektonchain_types.go)
  — new string field with JSON tag "storage.oci.encoding-format,omitempty".
  The existing AddConfigMapValues transformer picks this up automatically
  via reflection — no changes to transform.go or transformers.go.

• CRD validation (tektonchain_validation.go) — rejects values
  other than "", "dsse", and "sigstore-bundle" at admission time.

• Validation tests (tektonchain_validation_test.go) — invalid
  value is rejected; both valid values are accepted.

• Documentation (TektonChain.md, TektonConfig.md) — field
  added to the example YAML.

What was NOT changed

• transform.go / transformers.go — not needed (reflection)
• tektonchain_defaults.go — not needed (Chains defaults to dsse
  when the key is absent)
• No new dependencies

Related

• feat: add OCI 1.1 Referrers API support with configurable encoding format chains#1691 — feat: add OCI 1.1 Referrers API support
• fix(storage): forward RekorEntry to signature bundle in sigstore-bundle mode chains#1831 — fix: forward RekorEntry to signature bundle

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• Run make test lint before submitting a PR
• Includes tests (if functionality changed/added)
• Includes docs (if user facing)
• Commit messages follow commit message best practices

See the contribution guide for more details.

Release Notes

expose `storage.oci.encoding-format` config key in TektonChain and TektonConfig CRDs — allows configuring OCI 1.1 Referrers API storage via the operator

/kind feature

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 25.57%. Comparing base (241265e) to head (0572c35).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3871   +/-   ##
=======================================
  Coverage   25.56%   25.57%           
=======================================
  Files         455      455           
  Lines       23924    23926    +2     
=======================================
+ Hits         6116     6118    +2     
  Misses      17113    17113           
  Partials      695      695           

Flag	Coverage Δ
unit-tests	25.57% <ø> (+<0.01%)	⬆️

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[jkhelil]

hi @infernus01 Thanks for the PR

[jkhelil]

/approve

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jkhelil

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• OWNERS [jkhelil]

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[pratap0007]

/lgtm