refactor: rename Keycloak to RCIAM in group management documentation (#798)

- Rename folder from keycloak/ to rciam/
- Update linkTitle from 'Keycloak' to 'RCIAM' in main page
- Update all aliases to support both /keycloak/ and /rciam/ paths for
backward compatibility
- Update internal links in vos/_index.md to reference rciam instead of
keycloak
- Update section title from 'Keycloak' to 'RCIAM' in virtual
organisations overview

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# Summary

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**Related issue :**

---------

Co-authored-by: Enol Fernández <enol.fernandez@egi.eu>

Author: FerGonzalezPerez

.cspell.json

@@ -0,0 +1,50 @@
+{
+  "version": "0.2",
+  "language": "en",
+  "words": [
+    "RCIAM",
+    "rciam",
+    "Organisations",
+    "organisations",
+    "Organisation",
+    "organisation",
+    "organise",
+    "organised",
+    "behaviour",
+    "authorisation",
+    "Authorisation",
+    "virtualisation",
+    "organisational",
+    "Perun",
+    "perun",
+    "Keycloak",
+    "keycloak",
+    "aai",
+    "AAI",
+    "EGI",
+    "egi",
+    "VO",
+    "VOs",
+    "SAML",
+    "OIDC",
+    "OAuth",
+    "OpenID",
+    "IdP",
+    "SP",
+    "entitlements",
+    "subgroups",
+    "enrolment",
+    "enrolments",
+    "Enrolments",
+    "subgroup",
+    "vopersonid",
+    "mace",
+    "eduPersonPrincipalName",
+    "eduPersonOrgDN",
+    "infobox",
+    "visualise",
+    "visualised",
+    "categorised",
+    "customised"
+  ]
+}