Feature: Add support for pausing/resuming subscriptions

[pauloiankoski]

Resolves GIVE-1250

Description

This Pull Request adds supports for gateways to implement their solutions for pausing/resuming subscriptions. Within this PR we are:

• adding a new "paused" status to subscriptions;
• setting a color for the "paused" status in the subscriptions list table;
• adding a new SubscriptionPausable contract to be signed by gateways;
• adding a capability check as can_pause to gateways (false by default if not implemented);
• fixing the SubscriptionRepository to update the expiration date into the database;
• updating the subscription details screen to show the next renewal date for paused subscriptions as it does for active ones.

This PR is a foundational work that is required for the new implementations on Give Recurring.

Affects

Subscriptions

Pre-review Checklist

• Acceptance criteria satisfied and marked in related issue
• Relevant @unreleased tags included in DocBlocks
• Includes unit tests
• Reviewed by the designer (if follows a design)
• Self Review of code and UX completed

[JoshuaHungDinh]

Do we need this still?

[pauloiankoski]

No. That's a leftover.

[JoshuaHungDinh]

Just checking, everything seems to be in order with the UI and this work. This should be good to go! Would you prefer I make an epic for the UI & this or would you rather work off dev?

[JoshuaHungDinh]

Nice!

[jonwaldstein]

@pauloiankoski we decided to loosen the restriction on the SubscriptionPausable contract to receive an array of data instead of intervalInMonths - reason being want this to be flexible for other gateways and since this is our first gateway it's hard to predict what they will need.

[pauloiankoski]

Cool. That's something I was in doubt. I see other methods receiving a generic $gatewayData array instead.

[jonwaldstein]

@pauloiankoski yeah it's just hard to predict what params would be helpful for all gateways at this point, so i'd rather keep it flexible as changing signatures on contracts is painful 😄