### Motivation
Template 5 but with multiple tiers 😊
### Description
Enabling Template 7 by changing `7_disabled` to `7`
- Changed a `header.jpg` to `header.heic` to try and fix issue with
weirdly failing snapshot UI test
- Changed visibility on `TestData` from `public` to `internal`
- Hides tier selector if only one tier
- Changed `color_overrides_by_tier` to `colors_by_tier` and
`image_overrides_by_tier` to `images_by_tier`
- The original implementation was going to default to existing color and
images configurations and then override by tier
- However, this turned out to be harder to implement on the
configuration side
- `Colors` got four new optional values
- `tier_control_background`
- `tier_control_foreground`
- `tier_control_selected_background`
- `tier_control_selected_foreground`
### Demo
#### Full Screen
https://github.com/RevenueCat/purchases-ios/assets/401294/e5317a53-428c-415e-a1a1-b4231d32a776
### Footer
https://github.com/RevenueCat/purchases-ios/assets/401294/8905b55e-0fa2-49f0-aa1c-d4c1e694fb5b
### Footer Condensed
https://github.com/RevenueCat/purchases-ios/assets/401294/311d78fb-bdeb-43cd-b601-9c60a8a54b6f
This abstracts away the logic to ensure layouts are consistent when
selecting different packages in multi-package templates, in a way that
the content doesn't move around.
Josh Holtz