Add shortcut property to send modals via ApplicationContext

[krittick]

Summary

This adds a send_modal shortcut property to ApplicationContext to allow easier sending of modal dialogs instead of needing to use ctx.interaction.response.send_modal()

Examples were also updated to use the new method where appropriate.

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• If type: ignore comments were used, a comment is also left explaining why
• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, typehinting, examples, ...)

[Lulalaby]

Send modal sounds inappropriate
Maybe respond with modal?

[krittick]

Send modal sounds inappropriate
Maybe respond with modal?

I just kept it the same as the underlying method so it's easier for users to switch.

[krittick]

PR has been updated to make send_modal now return the Interaction object, which mirrors the behavior of send_message for consistency.