Ensure that release builds are built with cgo disabled.  This is usually the case for cross-compiled builds anyway, but adding this flag makes builds consistent regardless of what platform they are being built on.

In particular, without CGO_ENABLED=0, if you make the release builds on a linux/amd64 system then the linux/amd64 binary is dynamically linked against the system libc, meaning a binary built on a glibc-based system like Ubuntu will not work on a musl libc system like Alpine.  This is what appears to have happened for release 2.8.1.

But the same source code built on a different system (e.g. darwin/arm64) would cross-compile the linux/amd64 binary with cgo disabled, making a static binary that works on both glibc and musl systems.  This is what appears to have happened for release 2.8.2.

Setting CGO_ENABLED=0 in the Makefile will make the behaviour consistent for future releases, producing static binaries for the linux builds in all cases, whatever the build platform.

* chore: replace ioutil.ReadFile by os.ReadFile

* feat: Add two template functions

- cat:        Allows reading a value from a file
- credential: Allows reading a credential passed by systemd

`os.ReadFile` includes a trailing EOL, so we have to remove it to get
the correct value

* add ACR webhook to Hook-Examples.md

Incoming Azure Container Registry (ACR) webhook syntax and format with link to a working docker container used to handle webhook and feed a local registry cache

* Update Hook-Examples.md

changed text according to suggestions of  https://github.com/moorereason (see PR)

* Fix Gitea incoming webhook example and add a YAML version

* Fix payload-hmac-sha256 secret attribute name