feat: adding publisher agreement not signed message as page setting

[gnugomez]

Resolves #1548

[gnugomez]

@netomi As the message's wording closely aligns with the Eclipse Foundation's requirements, I’m adding it as a configurable component instead of creating separate variables for the agreement name and contact email. Does that approach seem suitable to you?

[netomi]

I think the approach is fine, however I have seen some other code also uses "Eclipse Foundation OpenVSX Publisher Agreement", we should have in the page settings a field:

export interface PageSettings {
    pageTitle: string;
    publisherAgreementName: string;

and use that consistently in the codebase imho.