Added AdditionalContent Parameter to Scheduler

[bikotoru]

This PR introduces a new parameter, AdditionalContent, to the scheduler component. It allows developers to add custom content next to the year, month, and day buttons, providing more flexibility for adding additional controls or information to the scheduler's header area.

Changes:

• Added AdditionalContent parameter of type RenderFragment.
• Updated documentation comments to describe the parameter's functionality.

This feature improves the customizability of the scheduler and addresses the need for more adaptable UI elements.

Please review the implementation and let me know if there are any changes needed.

[akorchev]

Hi @bikotoru,

Thank you for the PR. Can we think of a better name than AdditionalContent? It isn't clear where this additional content will go.

[bikotoru]

@akorchev
PersonalizedView?
CustomView?
AdditionalView?

I'm kind of bad with names haha

[akorchev]

What is the purpose of this to begin with? What do you want to add there?

[bikotoru]

@akorchev
For example a Refresh Button or ComboBox with Filters

[akorchev]

What bothers me is that it renders together with the default navigation (and the name). Somebody would ask for it to render before and not after. I can propose a different implementation - NavigationTemplate which replaces the whole navigation section - easier to name and provides full control. The existing navigation can be emulated with existing components too. What do you think?

[bikotoru]

@akorchev
perfect I have applied the change