[Fleet] Show SSL options for fleet server host in UI

[criamico]

Fleet Server currently allows some options to be configured on the CLI during bootstrapping of the agent in fleet server mode. These fields need to also be available in the UI so that the users can modify them during the life-cycle of the agent:

• Elasticsearch Certificate Authorities (optional)
• SSL certificate for Elasticsearch
• SSL certificate key for Elasticsearch
• Server SSL certificate authorities (optional)
• Client SSL certificate
• Client SSL certificate key

These options correspond to the following options sent to elastic agent:

FLAG	Description
–fleet-server-es-ca	CA to use for Elasticsearch connection
-fleet-server-es-cert	Fleet Server certificate to present to Elasticsearch
-fleet-server-es-cert-key	Fleet Server certificate key to present to Elasticsearch
–certificate-authorities	List of CA certificates that are trusted for when Elastic Agents connect to the fleet server
–fleet-server-cert	Fleet Server certificate to present to Elastic Agents during authentication
–fleet-server-cert-key	Fleet Server certificate key to present to Elastic Agents

Todo

• Store these settings in the fleet server host SO
• Show the new settings in the fleet server flyout (both when creating and editing a new fleet server host)
  • Ensure that a path to the cert (instead of cert itself) is inserted in the textbox
• Ensure that a warning is displayed any time a change is made to these UI elements, as changing the certificates can be disruptive for the user environment
• Ensure that a changed certificate/CA/key is reflected on the agent config

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[criamico]

@nimarezainia here's a preview of the new fields in the fleet server host "edit" flyout:

I am also working out a way to show these additional fields on the "add fleet server host" flyout and thought to add the new form fields inside a collapsible to avoid cluttering the flyout too much:

@simosilvestri what do you think about it?

[nimarezainia]

Looks good to me @criamico