fix: add alignment and focus related fixes for Shellbar

[InnaAtanasova]

Related Issue

Part of SAP/fundamental-ngx#4822 (NGX)

Description

• add example of Shellbar with Side Nav control button aka hamburger menu
• add proper alignment for the button (spacing)
• add fix for the focus color of the buttons used inside Shellbar, including Product Switch toggle

Screenshots

NOTE: If you've made any style changes, please provide appropriate screenshots (before and after) to help reviewers.

To see examples of which screenshots to include, go to Screenshot Examples.

Before:

After:

Please check whether the PR fulfills the following requirements

1. The output matches the design specs

• All values are in rem
• Text elements follow the truncation rules
• hover state of the element follow design spec
• focus state of the element follow design spec
• active state of the element follow design spec
• selected state of the element follow design spec
• selected hover state of the element follow design spec
• pressed state of the element follow design spec
• Responsiveness rules - the component has modifier classes for all breakpoints
• Includes Compact/Cosy/Tablet design
• RTL support

2. The code follows fundamental-styles code standards and style

• only one top level fd-* class is used in the file
• BEM naming convention is used
• Mixins are used for repeatable code (fd-rtl, fd-ellipsis, fd-flex, fd-selected, fd-focus, ect.)
• A11y support - keyboard support, screenreader support, proper ARIA attributes, etc.
• fd-reset() mixin is applied to all elements
• Variables are used, if some value is used more than twice.
• Checked if current components can be reused, instead of having new code.

3. Testing

• tested Storybook examples with "CSS Resources" normalize option
• tested Storybook examples with "CSS Resources" unnormalize option
• Verified all styles in IE11
• Updated tests
• last commit message should have [ci visual] so it can trigger chromatic visual regression (e.g. test: run chromatic visual regression [ci visual])

4. Documentation

• Storybook documentation has been created/updated
• Breaking Changes wiki has been updated in case of breaking changes.

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[JKMarkowski]

LGTM