[charts/portal] - Added support for configuring db node pool properties for portal container

[meetyourdev]

Description of the change Adding support for providing db node pool properties.

Benefits

Allows the user to provide environment variables to configure db node pool properties.

Drawbacks

Applicable issues

• fixes #

Additional information

Checklist

• [] Chart version bumped in Chart.yaml according to semver.
• [x] Variables are documented in the README.md
• [x] Title of the PR starts with chart name (e.g. [charts/gateway])
• [x] If the chart contains a values-production.yaml apart from values.yaml, ensure that you implement the changes in both files