docs: add Web Cloud Databases guide for enabling PostgreSQL extensions (#318)

* docs: add Web Cloud Databases guide for enabling PostgreSQL extensions

* docs: proofreading de db-enable-postgresql-extensions (fr)

- NBSP (U+00A0) avant deux-points et dans les guillemets (§6)
- Suppression de l'ellipse dans la description (unaccent… → etc.)
- Retrait de « intitulée » redondant (colonne « Extensions »)
- Bump lastUpdated → 2026-07-01

* docs: translate PostgreSQL extensions guide to en, de, es, it, pl, pt

* docs: proofreading db-enable-postgresql-extensions (7 locales)

- strip trailing period from description (de/es/it/pl/pt)
- align step 1 terminology on CP-NAV path: solution -> service (all locales)
- en: "the X concerned" -> "the relevant X"
- pt: "área de cliente" -> "Área de Cliente OVHcloud" (terminology CSV + L23)
- fr: NBSP before colon in CP-NAV labels

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Co-authored-by: Benoit Chuchla <benoit.chuchla@ovhcloud.com>