bug: signingAgent value needs to be updated

[Two-Hearts]

What is not working as expected?

The signingAgent is still Notation/1.0.0 under the released release-1.1 branch:

notation-go/signer/signer.go

Line 37 in 94a0e13

const signingAgent = "Notation/1.0.0"

What did you expect to happen?

The value should be notation-go/v1.1.1.

How can we reproduce it?

During signing.

Describe your environment

All env.

What is the version of your notation-go Library?

v1.1.1

[shizhMSFT]

We need to send out an PR to the main branch for RELEASE_CHECKLIST.md. Because of this field, the notation-go library requires a release process similar to notation CLI instead of notation-core-go.

Cross referencing: #437 (comment)

[Two-Hearts]

Closing as completed.