Update `fabric-ca` version in CLI project scaffolding

Currently, when running `galachain init `, to CLI will include a post-generate hook to modify the `fabric-ca` version:

https://github.com/GalaChain/sdk/blob/1d7aaccb3d5cf0af3e8efe7e11ea61725f86618f/chain-cli/network/fablo-post-generate.sh#L37

```
perl -i -pe 's/_CA_VERSION=1.5.0/_CA_VERSION=1.5.5/g' "$target_env"
```

I would like us to update this to at least version 1.5.6, because that is the first version of `fabric-ca` that provides a `linux/arm64` image in docker hub:

https://hub.docker.com/r/hyperledger/fabric-ca/tags

1.5.5 only provides `linux/amd64`, beginning with 1.5.6 builds for both `linux/amd64` and `linux/arm64` are available. Currently, this means to develop our SDK on a `linux/arm64` machine developers need to build the Fabric CA image manually, or manually tag version 1.5.6 as version 1.5.5.

Supporting Linux ARM VMs will be useful in streamlining the onboarding of new developers, some of whom may prefer to use a Linux VM on Apple Silicon, or may be using Linux on native ARM 64 hardware. And in the near future, potentially using Windows 11 on Arm-based PCs.

Given we appear to be using `fablo` version 2.0.0, I don't believe the above line will match the Fabric CA_VERSION string:

https://github.com/hyperledger-labs/fablo/blob/2.0.0/src/extend-config/extendGlobal.ts#L28

With 2.0.0, `fablo` appears to use Fabric CA version 1.5.5 by default.

I suspect changing the above line in our SDK to the following would set the Fabric CA version to 1.5.6 on `galachain init`:

```
perl -i -pe 's/_CA_VERSION=1.5.5/_CA_VERSION=1.5.6/g' "$target_env"
```

It would also be useful to add a section to our documentation explaining how to set environment variables that leverage fablo's built-in configuration options, in order to override these defaults in a local dev environment as needed.