[meta] add missing programming language tags to guides

[noave]

Some guides do not have any programming language tags like:

.. tag:: lang-nodejs

please add the tag(s) accordingly to the used programming languages in the tool. The folloing guides are missing the tags:

• [ ] source/guide_couchdb.rst
• [ ] source/guide_ejabberd.rst
• [ ] source/guide_eturnal.rst
• [ ] source/guide_focalboard.rst
• [ ] source/guide_gancio.rst
• [ ] source/guide_gotosocial.rst
• [ ] source/guide_influxdb2.rst
• [ ] source/guide_jellyfin.rst
• [ ] source/guide_keycloak.rst
• [ ] source/guide_libreoffice.rst
• [ ] source/guide_navidrome.rst
• [ ] source/guide_offen.rst
• [ ] source/guide_prosody.rst
• [ ] source/guide_resilio.rst
• [ ] source/guide_salt.rst
• [ ] source/guide_shellinabox.rst
• [ ] source/guide_tarsnap.rst
• [ ] source/guide_teamcity.rst
• [ ] source/guide_teamspeak.rst
• [ ] source/guide_vaultwarden.rst
• [ ] source/guide_wkd.rst