adding copyright header

[hghaf099]

This is to add the copyright header to Vault in the main branch and addresses this ticket
The copyright header is:

// Copyright (c) HashiCorp, Inc.
// SPDX-License-Identifier: MPL-2.0

As @ncabatoff suggested we can verify this by the following command.

git diff main...adding-copyright-header |grep -v '^---' | grep -v '^+++' |grep -v 'Copyright (c) HashiCorp, Inc.' |grep -v 'SPDX-License-Identifier: MPL-2.0' |grep -e '^[+-]' |sort -u

Running the above command results in the following diff:

+
+       $(SED) -i -e 's/Id/ID/' -e 's/SPDX-License-IDentifier/SPDX-License-Identifier/' vault/request_forwarding_service.pb.go
+       $(SED) -i -e 's/Idp/IDP/' -e 's/Url/URL/' -e 's/Id/ID/' -e 's/IDentity/Identity/' -e 's/EntityId/EntityID/' -e 's/Api/API/' -e 's/Qr/QR/' -e 's/Totp/TOTP/' -e 's/Mfa/MFA/' -e 's/Pingid/PingID/' -e 's/namespaceId/namespaceID/' -e 's/Ttl/TTL/' -e 's/BoundCidrs/BoundCIDRs/' -e 's/SPDX-License-IDentifier/SPDX-License-Identifier/' helper/identity/types.pb.go helper/identity/mfa/types.pb.go helper/storagepacker/types.pb.go sdk/plugin/pb/backend.pb.go sdk/logical/identity.pb.go vault/activity/activity_log.pb.go
+    "builtin/credential/aws/pkcs7/**",
+ */
+-->
+/**
+<!--
-       $(SED) -i -e 's/Id/ID/' vault/request_forwarding_service.pb.go
-       $(SED) -i -e 's/Idp/IDP/' -e 's/Url/URL/' -e 's/Id/ID/' -e 's/IDentity/Identity/' -e 's/EntityId/EntityID/' -e 's/Api/API/' -e 's/Qr/QR/' -e 's/Totp/TOTP/' -e 's/Mfa/MFA/' -e 's/Pingid/PingID/' -e 's/namespaceId/namespaceID/' -e 's/Ttl/TTL/' -e 's/BoundCidrs/BoundCIDRs/' helper/identity/types.pb.go helper/identity/mfa/types.pb.go helper/storagepacker/types.pb.go sdk/plugin/pb/backend.pb.go sdk/logical/identity.pb.go vault/activity/activity_log.pb.go
-    "builtin/credentials/aws/pkcs7/**",

The SED lines are the changes made to the Makefile for the proto target as there are replacements for "Id" into "ID". And, that also changes the copyright header. So, I have added another piece to the SED commands to revert the changes to the headers in those files.
Additional piece of change in the above diff is for "builtin/credential/aws/pkcs7/**". The change is in .copywrite.hcl file, and it was made because the original path was simply wrong as in there was no "builtin/credentials/aws/pkcs7/**".