fix: fusion helm changes

[saptarshi-datazip]

Description

Fusion helm chart improvements for credential management, external Postgres compatibility and init container cleanup.

Changes:

• Remove fusion.adminUser / fusion.adminPassword — Fusion and olake-ui now use olakeUI.initUser credentials (or existingSecret) as the single source of truth
• Fix Fusion JDBC URL for external Postgres by coercing port with toString (fixes %!s(float64=5432) rendering failure)
• Skip create-fusion-database init container when using external Postgres (no longer pulls bundled Postgres image for a connectivity-only check)

Fixes minor bugs and optimizations

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (needs rollout restart of ui for upgrading users after the fusion pods restarts; this is for Signature check failure)
• This change requires a documentation update (need to remove the customization for admin in fusion helm if there)

How Has This Been Tested?

• Fresh install with Fusion enabled — default credentials, catalogs/tables list in Maintenance
• Upgrade from stable chart with custom fusion.adminUser / fusion.adminPassword — verified credential migration path to olakeUI.initUser
• External Postgres with numeric port: 5432 — Fusion JDBC URL renders correctly, pod reaches Running
• External Postgres — create-fusion-database init container not deployed; bundled Postgres still creates fusion DB when postgresql.enabled: true
• helm template sanity checks for JDBC URL, init container presence and credential secret refs

Screenshots or Recordings

Related PR's (If Any):