Introduce is_woo_express_trial_plan function

[PanosSynetos]

Changes proposed in this Pull Request:

Introduce a new function is_woo_express_trial_plan to be used by

• Introduce a remote inbox rule for Woo Express sites woocommerce/woocommerce#40513 (comment)

Closes #1350 .

• This PR is a very minor change/addition and does not require testing instructions (if checked you can ignore/remove the next section).

How to test the changes in this Pull Request:

• Have you followed the Writing high-quality testing instructions guide?

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?

FOR PR REVIEWER ONLY:

• I have reviewed that everything is sanitized/escaped appropriately for any SQL or XSS injection possibilities. I made sure Linting is not ignored or disabled.

[github-actions]

Size Change: 0 B

Total Size: 196 kB

ℹ️ View Unchanged

Filename	Size
./build/53.js	1.05 kB
./build/index.css	883 B
./build/index.js	121 kB
./build/marketing.js	58 kB
./build/payment-gateway-suggestions.css	1.25 kB
./build/payment-gateway-suggestions.js	6.45 kB
./build/plugins.js	3.92 kB
./build/style-index.css	2 kB
./build/style-marketing.css	805 B

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