1. Proposed title of this feature request

Secure way to add Hashicorp Vault token when integrating with Tekton Chains

2. What is the nature and description of the request?

Customer is integrating Hashicorp vault with Tekton Chains and needs a secure way to pass vault token. At present the token value is added to TektonConfig using `signers.kms.auth.token` field.

3. Why does the customer need this? (List the business requirements here)
4. List any affected packages or components.