Run postgresql integration test on latest chart

[mabhi]

Change Overview

Integration tests for postgres were failing for postgresql app with latest helm chart.
This PR reverts to the latest working version of postgres helm chart from earlier temporary fix version i.e 12.6.0 for the test app.

Generate random password as following were being ignored

• global.postgresql.auth.postgresPassword
• auth.postgresPassword
  Bug was reported for the same at bitnami/postgresql. New chart version fixed the issue.

Depends on: #2206

Pull request type

Please check the type of change your PR introduces:

• 🚧 Work in Progress
• 🌈 Refactoring (no functional changes, no api changes)
• 🐹 Trivial/Minor
• 🐛 Bugfix
• 🌻 Feature
• 🗺️ Documentation
• 🤖 Test

Issues

• fixes [BUG] Integration tests failing for PostgreSQL application #2155

Test Plan

Successfully ran integration tests for PostgreSQL application

./build/integration-test.sh ^PostgreSQL$
Running integration tests:
...
...
...
{"File":"pkg/app/postgresql.go","Function":"github.com/kanisterio/kanister/pkg/app.PostgresDB.Uninstall","Line":199,"app":"postgres","cluster_name":"4e3c7620-4569-4d87-8f7d-0f22884ca1ed","level":"info","msg":"Uninstalling helm chart.","namespace":"postgres-test","release":"postgres-cdqkp","time":"2023-07-19T10:24:25.000370184+05:30"}
OK: 1 passed
--- PASS: Test (68.09s)
PASS
ok      github.com/kanisterio/kanister/pkg/testing      68.132s

• 💪 Manual
• ⚡ Unit test
• 💚 E2E

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[PrasadG193]

We can remove this line

[mabhi]

Removed