Update copyright headers

[praveenrewar]

Describe the problem/challenge you have
Currently the copyright headers for all the tools say:

// Copyright 2023 VMware, Inc.
// SPDX-License-Identifier: Apache-2.0

Describe the solution you'd like
Now that Carvel is a CNCF project, it should be something like

// Copyright 2023 The Carvel Authors.
// SPDX-License-Identifier: Apache-2.0

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