This adds functionality that enables the default publisher to
publish SBOMs (and later signatures and attestations) when the
`build.Result` is an `oci.SignedEntity`.
This also changes the `gobuild` logic to start producing
`oci.Signed*` as its `build.Result`s, so when executed we get an
SBOM for each architecture image.
For example, see the "Published SBOM" lines below:
```shell
2021/11/19 19:24:50 Using base gcr.io/distroless/static:nonroot for github.com/google/ko
2021/11/19 19:24:51 Building github.com/google/ko for linux/amd64
2021/11/19 19:24:52 Building github.com/google/ko for linux/arm64
2021/11/19 19:24:57 Publishing ghcr.io/mattmoor/ko:latest
2021/11/19 19:24:58 existing blob: sha256:c78c74e7bb4a511f7d31061fbf140d55d5549a62d33cdbdf0c57ffe43603bbeb
2021/11/19 19:24:58 existing blob: sha256:4aa59d0bf53d4190174fbbfa3e9b15fdab72e5a95077025abfa8435ccafa2920
2021/11/19 19:24:58 ghcr.io/mattmoor/ko:sha256-d2bc030f5ed083d5e6a30a7969c9a8e599511b8d7a6e20695bf5ea029b6e2c3f.sbom: digest: sha256:c67ec671aaa82902e619883a7ac7486e6f9af36653449e2eb030ba273fe5a022 size: 348
2021/11/19 19:24:58 Published SBOM ghcr.io/mattmoor/ko:sha256-d2bc030f5ed083d5e6a30a7969c9a8e599511b8d7a6e20695bf5ea029b6e2c3f.sbom
2021/11/19 19:24:58 existing blob: sha256:c78c74e7bb4a511f7d31061fbf140d55d5549a62d33cdbdf0c57ffe43603bbeb
2021/11/19 19:24:58 existing blob: sha256:4aa59d0bf53d4190174fbbfa3e9b15fdab72e5a95077025abfa8435ccafa2920
2021/11/19 19:24:59 ghcr.io/mattmoor/ko:sha256-b74c230f20efd94981e5fd823bacc23cbd71055a1b3b6a0893152b398c67743b.sbom: digest: sha256:c67ec671aaa82902e619883a7ac7486e6f9af36653449e2eb030ba273fe5a022 size: 348
2021/11/19 19:24:59 Published SBOM ghcr.io/mattmoor/ko:sha256-b74c230f20efd94981e5fd823bacc23cbd71055a1b3b6a0893152b398c67743b.sbom
2021/11/19 19:24:59 existing blob: sha256:3f7e3c6765a6abc682cd40ea256fbea5c1d4debbc07659efbc0dedc13eee0da6
2021/11/19 19:24:59 existing blob: sha256:250c06f7c38e52dc77e5c7586c3e40280dc7ff9bb9007c396e06d96736cf8542
2021/11/19 19:24:59 existing blob: sha256:e8614d09b7bebabd9d8a450f44e88a8807c98a438a2ddd63146865286b132d1b
2021/11/19 19:24:59 existing blob: sha256:7067b1bc6f9ce59f3a4ed2216946ebbb27a4f7a102f55d96c6af1dc90e77b510
2021/11/19 19:25:00 ghcr.io/mattmoor/ko@sha256:d2bc030f5ed083d5e6a30a7969c9a8e599511b8d7a6e20695bf5ea029b6e2c3f: digest: sha256:d2bc030f5ed083d5e6a30a7969c9a8e599511b8d7a6e20695bf5ea029b6e2c3f size: 751
2021/11/19 19:25:01 existing blob: sha256:250c06f7c38e52dc77e5c7586c3e40280dc7ff9bb9007c396e06d96736cf8542
2021/11/19 19:25:02 pushed blob: sha256:121c637d5c84562b51404a6f71c1f995ad059740293a3911a0dc33eb223e41a4
2021/11/19 19:25:02 pushed blob: sha256:859e03b7461b2a512159493ef1504d2859ed37c05ed1ef781ff98394ea4799b5
2021/11/19 19:25:02 pushed blob: sha256:d1b55c3db0f16b5056776c6d2c279efd16d28dbf1aae3eef1f3f9b7551d1f490
2021/11/19 19:25:03 ghcr.io/mattmoor/ko@sha256:b74c230f20efd94981e5fd823bacc23cbd71055a1b3b6a0893152b398c67743b: digest: sha256:b74c230f20efd94981e5fd823bacc23cbd71055a1b3b6a0893152b398c67743b size: 751
2021/11/19 19:25:03 ghcr.io/mattmoor/ko:latest: digest: sha256:e4466a7dd9be66c7c1b43a8ecc19247041ece232407a14e3d6ea3c51d2561a71 size: 529
2021/11/19 19:25:03 Published ghcr.io/mattmoor/ko@sha256:e4466a7dd9be66c7c1b43a8ecc19247041ece232407a14e3d6ea3c51d2561a71
ghcr.io/mattmoor/ko@sha256:e4466a7dd9be66c7c1b43a8ecc19247041ece232407a14e3d6ea3c51d2561a71
```
The "SBOM" being attached in this change is the raw output of `go version -m`,
which we will convert to one of the standard formats in a subsequent change.
* Build working Windows container images
Add e2e tests that run on Windows and cover kodata behavior
* now successfully skipping symlinks on windows :-/
* fix e2e test on windows, that relied on a symlink in kodata after all
* document windows symlink issue
* review feedback
* re-add kodata symlink tests for linux
* Move ko binary to root of project.
* go.mod says required golang version is 1.14
* go install uses the folder name
* lint and copyright bump
* moving the test file changed the test hash.
* more refs of cmd/test
* add deprecation message
