Update template-related messages to improve clarity for custom post types

[snehapatil2001]

closes #67697

What?

This PR updates template-related messages in the Gutenberg editor to use generic phrasing, removing references to specific post types like "posts" and "pages."

Why?

Template messages previously referred to "posts" and "pages," which could be confusing when working with custom post types or templates shared across different post types (e.g., products, orders). This change ensures the messages are more inclusive and clear for all scenarios.

How?

• Updated the dialog text when selecting a template block in template-lock mode to avoid post-type-specific references.
• Revised the Save Changes sidebar description to use generic phrasing, referring to "other parts of your site" instead.

Testing Instructions

1. Open the Gutenberg editor.
2. Select a template block that is part of a locked template.
3. Verify the updated dialog message appears.
4. Make a change to a template and open the Save Changes sidebar.
5. Verify the updated Save Changes sidebar message appears.

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Co-authored-by: snehapatil2001 <snehapatil02@git.wordpress.org>
Co-authored-by: youknowriad <youknowriad@git.wordpress.org>

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[youknowriad]

Would love a confirmation for the copy here. But it's a good change IMO