Deprecate props on the swisspost-internet-header that will be removed in v10

[gfellerph]

A couple of props that are now available on the swisspost-internet-header will no longer be available in v10. Add a deprecation notice to the v9 docs that informs about the upcoming changes. Place an inline hint in the props table of storybook for each prop. The notification should state the reason for removal and the alternative if any.

Please refer to #6275, #6873 and #6872 for detailed implementation tickets for v10.

Header

• activeRoute: boolean type is replaced by string "none" for false and "auto" for true. Otherwise, activeRoute prop will remain unchanged.
• languageCookieKey: Used to set cookie key for the current language cookie. Deprecated in favour of project specific solution due to low usage.
• languageLocalStorageKey: Used to set local storage language information. Deprecated in favour of project specific solution due to low usage.
• login: Use the new configuration API to show/hide the login
• logoutURL: Use the new configuration API to specify logout URL
• meta: Use the new configuration API to show/hide meta navigation links
• search: Use the new configuration API to show/hide the search
• stickyness: This option is no longer configurable with the new header
• fullWidth: Use the self-managed header for applications
• skiplinks: Please implement the skiplinks component (-> should the header keep handling this or not?)
• customConfig: Use the main navigation slot provided to add custom menu entries
• languageSwitchOverrides: Use the language-menu slot to override the rendered language switch to specify custom URLs for each language
• osFlyoutOverrides: New header does not provide this flyout anymore. Use the main navigation slot to add application specific menu items
• selfAdminOrigin: use the new API to provide these URLs
• configProxy: no longer provided functionality, has been deprecated before
• getCurrentLanguage: use document.documentElement.lang instead

Breadcrumbs

• hide-buttons: Help and Contact buttons are no longer provided, this prop is therefore no longer necessary.
• toggleOverlayById: Overlays are no longer provided, this method is therefore no longer necessary.

Footer

• customConfig: Use the new API to specify footer links in all four columns. This prop is no longer provided