Update psammead-navigation to take in colours

[sareh]

Is your feature request related to a problem? Please describe.
Currently Psammead-navigation has hard-coded colours for:

C_WHITE - text and hover/focus colours
C_POSTBOX - background on navigation
Unnamed color '#eab3b3'; - border colour on nav items (white with 30% transparency over C_POSTBOX) - we should add this into Psammead Assets as a named colour. https://bbc.github.io/psammead/?path=/story/utilities-psammead-styles--colours

We should ensure we pass in these colours as props, so that we can then use Learning English colours for their navigation. e.g. C_LE_TEAL for navigation background, C_WHITE for text and hover/focus colours & following on from the pattern used above, a new hex colour for white with 30% transparency over C_LE_TEAL.

Describe the solution you'd like

• We should ensure we add all relevant new colours to psammead-assets
• Add colour themes to storybook helpers, so they're available for storybook (e.g. when you select learningenglish as a service, you have navigationColour value set to correct constant)
• We should add props / enable theming for the psammead-navigation component.
• Ensure Storybook and Tests are passing in the colour props.

This should be a major version update, since it should make the colours required props.
Then a Simorgh PR is needed to update Simorgh to use these, add colours into Service Config files and use them in the application by passing them to psammead-navigation.

Describe alternatives you've considered
N/A

Testing notes
[Tester to complete]

Dev insight: Will there be any potential regression? etc

• This feature is expected to need manual testing.

Additional context
Add any other context or screenshots about the feature request here.