Remove redundunt self-signed-cert secret

[mmorhun]

Is your task related to a problem? Please describe.

For now, in case of using self-signed certificate user must provide precreated one.
But internally we use che-tls secret for securing routes and also use self-signed-cert for propagating CA certificate to Che components to trust the self-signed certificate. This is redundant and we can use only one secret che-tls which must have ca.crt field in case of self-signed certificate.

Describe the solution you'd like

Remove self-signed-cert secret and use che-tls instead. In case of manually generated by a user self-signed certificate and putting precreated secret, we should require ca.crt field in it.

Additional context

Cert Manager puts ca.crt in its secrets automatically.

[tolusha]

@mmorhun
How is important this task is for TLS by default?
Is it something we can fix by ourselves?

[mmorhun]

@tolusha I found this problem while I was working on #15313. This issue doesn't block TLS by default but brings need for additional effort in implementation. Also may ran into it later, so I would like to resolve it to have code clean and clear to understand.

[mmorhun]

I think, I will handle this issue now, because the cost for workaround roughly equal to the cost of the fix...

[mmorhun]

Done