[BeatsCM] Add user flow for managing TSL certs

[mattapperson]

Due to the need for Beats to communicate securely with Kibana, we need users to setup certs on the host beats run on so it can trust Kibana. This process has proven tedious for users, so we want to introduce a UI to manage this process.

We will need an initial step where instructions are provided and a cert text input block is provided in order to let users add their cert to BeatsCM for later use.

We will also need a management screen to delete/add a new cert.

• There can only be one cert at a time
• We might be able to get the cert from kibana, but most often not. (ability to inform the user without requiring action
• Users can't see/edit the cert, only add/remove/replace it.
• Users will need to be able to name the cert (optional) and know the date it was added

[ryankeairns]

Design meeting notes

• can sometimes get SSL cert from Kibana to establish a secure connection
  • pull from ES settings (if kibana and ES running on same machine; not typical)
  • the check is instant, we know right away
• when we can get it, let user know it was successfully found
• when we can't, we need a screen that says...
  • "upload here" (provide instructions (CLI); copy paste into textarea
    • users won't be generating, they'll already haven one
    • similar to "Checking for existing SSH keys" on github
  • "we'll store it securely"
  • confirm it was stored
• part of initial walkthrough
  • on or before the 'Enroll beat' screen under Advanced Settings

[ph]

This needs a bit more thinking on our side, so I would not do it right now.
We still need to move to use a web token and we can revisit the experience after.