Add resource values for nginx and postgres

[davejab]

Desired Outcome

Expose chart values to set resource requests and limits on nginx + postgres pods.

Implemented Changes

Resource value configuration has been exposed allowing users to customise requests + limits for nginx + postgres pods. This was a requirement for our cluster as we have strict policies in place that require all pods to have resources defined.

Connected Issue/Story

n/a

Definition of Done

At least 1 todo must be completed in the sections below for the PR to be
merged.

Changelog

• The CHANGELOG has been updated, or
• This PR does not include user-facing changes and doesn't require a
  CHANGELOG update

Test coverage

• This PR includes new unit and integration tests to go with the code
  changes, or
• The changes in this PR do not require tests

Documentation

• Docs (e.g. READMEs) were updated in this PR
• A follow-up issue to update official docs has been filed here: [insert issue ID]
• This PR does not require updating any documentation

Behavior

• This PR changes product behavior and has been reviewed by a PO, or
• These changes are part of a larger initiative that will be reviewed later, or
• No behavior was changed with this PR

Security

• Security architect has reviewed the changes in this PR,
• These changes are part of a larger initiative with a separate security review, or
• There are no security aspects to these changes

[szh]

Hi @davejab,

Thank you for submitting this PR. It looks great but we need to have a test case before we can merge it. We're currently evaluating how to refactor our tests in this repository so we can easily add test cases. In the meantime I'll leave this PR open and we'll get back to it once we rework the tests.