Switch option: calculate yearly savings dynamically

[nalcalag]

Task/Issue URL: https://app.asana.com/1/137249556945/project/1211755920811451/task/1211842214579233?focus=true

Description

Calculate savings dynamically from product details fetched

Steps to test this PR

Pre steps

• Apply patch from https://app.asana.com/1/137249556945/project/1209991789468715/task/1210448620621729?focus=true

Upgrade

• Install from branch
• Purchase a test monthly subscription (Free Trial)
• Cancel and wait until Free Trial expires OR wait until free trial is renewed to a paid monthly subscription
• If expired after canceled, purchase a monthly subscription again
• Go to Subscription Settings
• Check Switch option is there with updated text "Switch to Yearly and Save 17%"
• Select Switch option
• Check copy for upgrade option is correct (17%)

Downgrade

• Switch to yearly
• Wait until screen refreshes
• Select switch option
• Check copy for downgrade option is correct (17%)

No UI changes

[nalcalag]

FYI: I have another branch to handle translations

[lmac012]

LGTM