fix(jsx-email): change how package.json is read so it doesn't break with recent node versions

[isaacdonaldson]

Component / Package Name: jsx-email

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

If yes, please include "BREAKING CHANGES:" in the first commit message body, followed by a description of what is breaking.

List any relevant issue numbers:

Description

Node v22 deprecated the use of the assert { type: 'json' } syntax when importing modules in favour of the with { type: 'json' } syntax (they are used when reading JSON). The assert syntax was used up until v22, and the with syntax started being supported in node v18.20. jsx-email supports version 18.19+ meaning using the with syntax would be a breaking change.

The reading of JSON was happening when the cli tool was reading from the package.json. This PR introduces the change that instead of reading the package.json as a module, we read it inside a .cts file which does not use the same assert/with syntax.

This PR is a little tricky to test (and why there are no test cases added), but it looks to work on node versions: 18.19.0, 18.20.0, and 22.6.0. I don't believe any issues should occur because the "esModuleInterop" option in the tsconfig.json is set to true, but some extra care wouldn't hurt.

[shellscape]

Thanks for making this happen. Sorry that I wasn't able to get to merging it until now - we just got power back on today. Hurricanes are bananas.