feat: Provide branding for the Welcome page

[RomanNikitenko]

depends on #219

What does this PR do?

Provides branding for the Welcome page:

• value of the welcomePageTitle field is used as the Welcome page title
• value of the nameLong filed is used as the Welcome page title if the welcomePageTitle field is not provided
• value of the welcomePageSubtitle field is used as the Welcome page subtitle
• default value from the upstream is used as the Welcome page subtitle if the welcomePageSubtitle field is not provided
• nameLong is still used for the About dialog and browser tab title

demo.Roman.welcome.page.branding.mp4

What issues does this PR fix?

https://issues.redhat.com/browse/CRW-4114

How to test this PR?

• provide the corresponding fields to the product.json file
• build an assembly
• check that the corresponding changes are applied for the Welcome page

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Pull Request images published ✨
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[github-actions]

Pull Request images published ✨
image: quay.io/che-incubator-pull-requests/che-code:pr-223-amd64
Dev image: quay.io/che-incubator-pull-requests/che-code-dev:pr-223-dev-amd64

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Build 3.7 :: code_3.x/648: Console, Changes, Git Data

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Build 3.7 :: sync-to-downstream_3.x/3380: Console, Changes, Git Data

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Build 3.7 :: get-sources-rhpkg-container-build_3.x/3178: Console, Changes, Git Data

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