Feature/configurable expire headers for static assets

[phoenix-bjoern]

Related issues

#3268

closes #

Short description and why it's useful

Added a new configuration expireHeaders to define max-age per mime type:

"expireHeaders": { "default": "30d", "application/json": "24h", "image/png": "7d" }

If there is no setting for the mime type it uses the default value.
Note that if the NODE_ENV isn't "production" the max-age setting will be 0 (which is helpful during development to not deal with browser cache invalidation). So to test the functionality you should switch to production mode.

Screenshots of visual changes before/after (if there are any)

Which environment this relates to

Check your case. In case of any doubts please read about Release Cycle

• Test version (https://test.storefrontcloud.io) - this is a new feature or improvement for Vue Storefront. I've created branch from develop branch and want to merge it back to develop
• RC version (https://next.storefrontcloud.io) - this is a stabilisation fix for Release Candidate of Vue Storefront. I've created branch from release branch and want to merge it back to release
• Stable version (https://demo.storefrontcloud.io) - this is an important fix for current stable version. I've created branch from hotfix or master branch and want to merge it back to hotfix

Upgrade Notes and Changelog

• No upgrade steps required (100% backward compatibility and no breaking changes)
• I've updated the Upgrade notes and Changelog on how to port existing VS sites with this new feature

IMPORTANT NOTICE - Remember to update CHANGELOG.md with description of your change

Contribution and currently important rules acceptance

• I read and followed contribution rules
• I read the TypeScript Action Plan and adjusted my PR according to it
• I read about Vue Storefront Modules and I am aware that every new feature should be a module

[patzick]

Nice feature, i've seen that in action :)

[lukeromanowicz]

Looks awesome! one small improvement could be done but overall it's exactly what we need 👍