docs(apidoc): filter Optional markers from validation column (#723)

The crd-ref-docs tool v0.3.0 started rendering `+optional` Go markers as
`Optional: {}` in API documentation's validation column. This appeared
as redundant empty JSON objects since the Required column already
conveyed this information. The PR updates the documentation template to
filter these markers while keeping meaningful validation rules like
patterns and enums, and removes unnecessary customMarkers configuration.

Closes #722

Signed-off-by: Marco Nenciarini <marco.nenciarini@enterprisedb.com>

Taskfile.yml

@@ -86,7 +86,7 @@ tasks:
       # renovate: datasource=git-refs depName=crd-gen-refs lookupName=https://github.com/cloudnative-pg/daggerverse currentValue=main
       DAGGER_CRDGENREF_SHA: ee59e34a99940e45f87a16177b1d640975b05b74
       # renovate: datasource=go depName=github.com/elastic/crd-ref-docs
-      CRDREFDOCS_VERSION: v0.2.0
+      CRDREFDOCS_VERSION: v0.3.0
     cmds:
       - >
         GITHUB_REF= dagger -s call -m github.com/cloudnative-pg/daggerverse/crd-ref-docs@${DAGGER_CRDGENREF_SHA}

hack/crd-gen-refs/config.yaml

@@ -1,9 +1,6 @@
 processor:
   ignoreGroupVersions:
     - "GVK"
-  customMarkers:
-    - name: "optional"
-      target: field
   ignoreFields:
 #    - "status$"
     - "TypeMeta$"

hack/crd-gen-refs/markdown/type.tpl

@@ -31,7 +31,7 @@ _Appears in:_
 {{ end -}}
 
 {{ range $type.Members -}}
-| `{{ .Name  }}` _{{ markdownRenderType .Type }}_ | {{ template "type_members" . }} | {{ if not .Markers.optional -}}True{{- end }} | {{ markdownRenderDefault .Default }} | {{ range .Validation -}} {{ markdownRenderFieldDoc . }} <br />{{ end }} |
+| `{{ .Name  }}` _{{ markdownRenderType .Type }}_ | {{ template "type_members" . }} | {{ if not .Markers.optional -}}True{{- end }} | {{ markdownRenderDefault .Default }} | {{ range .Validation -}}{{- $v := markdownRenderFieldDoc . }}{{- if and $v (ne $v "Optional: \\{\\}") -}} {{ $v }} <br />{{ end }}{{- end }} |
 {{ end -}}
 
 {{ end -}}