feat: action v2 signing (#8779)

# Which Problems Are Solved

The action v2 messages were didn't contain anything providing security
for the sent content.

# How the Problems Are Solved

Each Target now has a SigningKey, which can also be newly generated
through the API and returned at creation and through the Get-Endpoints.
There is now a HTTP header "Zitadel-Signature", which is generated with
the SigningKey and Payload, and also contains a timestamp to check with
a tolerance if the message took to long to sent.

# Additional Changes

The functionality to create and check the signature is provided in the
pkg/actions package, and can be reused in the SDK.

# Additional Context

Closes #7924

---------

Co-authored-by: Livio Spring <livio.a@gmail.com>

docs/package.json

@@ -17,7 +17,7 @@
     "generate:grpc": "buf generate ../proto",
     "generate:apidocs": "docusaurus gen-api-docs all",
     "generate:configdocs": "cp -r ../cmd/defaults.yaml ./docs/self-hosting/manage/configure/ && cp -r ../cmd/setup/steps.yaml ./docs/self-hosting/manage/configure/",
-    "generate:re-gen": "yarn clean-all && yarn gen-all",
+    "generate:re-gen": "yarn generate:clean-all && yarn generate",
     "generate:clean-all": "docusaurus clean-api-docs all"
   },
   "dependencies": {