Develop two variants of the Install new Agent modal

What does this MR do and why?

Currently, we have the create agent button disabled if there're no agent configurations in the current project.

As we are changing the Kubernetes section UX, we want to add an actions dropdown where the 'Register new Agent' button will be always available. That's why we want to develop two variants for the registration popup:

1. If there're no configurations present in the project it should say 'Install new Agent' and contain links to the docs
2. If the configurations are present it should say 'Connect with Agent' and show the dropdown with the available agent configurations.

This MR is a part of the revisiting the Kubernetes section issue that contains the following steps:

1. Move clusters_empty_state component to Vue --> !73064 (merged)
2. Change the navigation for the new cluster page --> !73163 (merged)
3. Change the copy and empty state illustrations in the existing components --> !73586 (merged)
4. Add an empty state variant for the Install new Agent modal <-- \textcolor{#FC6D26}{\textsf{You are here}}
5. Change the navigation on the clusters page to Vue and actions button on the top of the page (introducing the clusters_main_view and clusters_actions components --> !73637 (merged)
6. Add the 'All' tab --> !74135 (merged)

More information is in the main MR(!71482 (closed))

Screenshots or screen recordings

No Agent configurations present

An Agent configuration is present

Step 1:

Step 2:

How to set up and validate locally

1. Visit Integrations > Kubernetes clusters page
2. Click the Actions button
3. To create an agent configuration, follow this guide. Please note, that the agent name should not contain underscores or dots.

MR acceptance checklist

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Related to #340759 (closed)