Restore latest apps versions from k3sup

The original version of arkade was based upon k3sup 0.8.10
which missed some changes from the community.

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <[email protected]>

Add the option to use Staging LE issuer for OpenFaaS Ingress

We may want to test that the app will correctly issue a cert but not
actually get a prod cert. You are limited to 30 new sub-domains a week with
LE.
This lets you pass the --staging flag to `arkade install
openfaas-ingress --staging`

Signed-off-by: Alistair Hey <[email protected]>

Tidy go-mod

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <[email protected]>

Update default from helm2 to helm3 in info message

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <[email protected]>

Update fmt target

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <[email protected]>

Revise readme

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <[email protected]>