Rely on the vX.X.X tag naming scheme to make it easier to import the ECK Go module as a dependency

[naemono]

See #5809 (comment)

Even after moving to a /v2 go module path in go.mod, we are still being imported using a legacy format:

❯ go get github.com/elastic/cloud-on-k8s/v2@2.4.0
go: added github.com/elastic/cloud-on-k8s/v2 v2.0.0-20220812092235-96282ca98df1

We need to adjust our release process to ensure we are prefixing releases/tags with v, such as v2.6.0.

Things to consider:

• Redhat release process changes needed.
• Documentation noting the change, as not to confuse someone wanting to install a previous version, only to find it's not prefixed with v.
• ECK Helm chart changes.
• Tooling changes needed under hack directory? (release-notes, upgrade-test-harness, update-stack-version.sh)
• CI changes?
• Public facing documentation changes (kubectl install links; release notes links)

[thbkrkr]

For the go module import to work properly, we need to create the git tag with the v prefix. Am I correct if I say that we do not need to have this v elsewhere? So, couldn't we just remove the v prefix where we use the git tag and continue as before? It would only involve one small change, nothing more, because the tag is only used in one place (when .ci/setenvconfig build is called).

diff --git a/.ci/setenvconfig b/.ci/setenvconfig
index b986f6eab5..2ef1caef1b 100755
--- a/.ci/setenvconfig
+++ b/.ci/setenvconfig
@@ -686,7 +686,7 @@ GO_TAGS=release
 export LICENSE_PUBKEY=${PROJECT_PATH}/.ci/license.key

 SNAPSHOT=false
-IMG_VERSION=$TAG_NAME
+IMG_VERSION=${TAG_NAME#"v"} # remove v prefix
 ENV