[frameit] Add force_resize_background option

[kdo1234]

Checklist

• I've run bundle exec rspec from the root directory to see all new and existing tests pass
• I've followed the fastlane code style and run bundle exec rubocop -a to ensure the code style is valid
• I've read the Contribution Guidelines
• I've updated the documentation if necessary.

Motivation and Context

This pull request increases developer control on how background images are used for framed screenshots.

Description

This pull request preserves frameit's default behavior in which the background image is resized keeping the aspect ratio if the height of the background image does not equal the height of the screenshot.
This pull request adds a new configuration setting named force_resize_background to frameit.
If force_resize_background is set to true then frameit always resizes the background image ignoring aspect ratio (i.e. regardless of whether the height of the background equals the height of the screenshot).

Testing Steps

I ran the existing tests.
I ran frameit locally with the configuration set to true and false and not set, and observed that the resulting framed screenshots were as expected.

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[janpio]

Looks interesting @kdo1234 - can you take care of the CLA?

[kdo1234]

Looks interesting @kdo1234 - can you take care of the CLA?

I'll figure out how to accept the CLA, right not the issue with accepting the CLA is that my github doesn't have a public email address.

Do you think the project will accept this pull request?

Thank you

[janpio]

If you can tell me a bit more why this option is useful and when you might want to use it, I am pretty sure we can merge this (CLA required of course).

[joshdholtz]

@kdo1234 Heyyy 👋 I'm good to merge this if you are able to accept the CLA 😊

[joshdholtz]

@kdo1234 One more ping on accepting the CLA 🙏

[UInt2048]

@kdo1234 Attempting to ping you in case you figured it out! ;)