Added empty state messages in breadcrumb selectors (Header)

[ShailRT]

Description

This PR fixes #4099 and displays a message when there are no items in breadcrumb selector.

Database selector:

• When there are no databases, it display a "No Databases configured" text in the dropdown.
• We display a peristent link to "Connect a database".

Schema selector:

• When there are no schemas, we display a "No Schemas configured" text in the dropdown.

Table selector:

• When there are no tables, we display a "No Tables configured" text in the dropdown.

Screenshot

Before (No Database):

After (No Database):

Before (No Schema):

After (No Schema):

Before (No Table/Exploration):

After (No Table/Exploration):

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the develop branch of the repository
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

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