Centralise how tests initialise Forge app

[knolleary]

Fixes #770

Reduces code duplication and ensures all tests are enabled for postgres testing

The basic pattern for tests to follow is:

// Load the common test utils module
const FF_UTIL = require('flowforge-test-utils')

// Initialise the app with whatever config is required
const app = await FF_UTIL.setupApp({
    license: '....'
})

The FF_UTIL.setupApp function includes a default app config suitable for most tests. The passed-in configuration augments (rather than replaces) that default config.

It also contains the logic to insert the postgres db config if the appropriate env vars are set to enable postgres testing.

[knolleary]

As of this PR, the default test configuration is:

{
        telemetry: { enabled: false },
        logging: {
            level: 'warn'
        },
        db: {
            type: 'sqlite',
            storage: ':memory:'
        },
        email: {
            enabled: true,
            transport: new LocalTransport()
        },
        driver: {
            type: 'stub'
        },
        broker: {
            url: ':test:'
        }
}