Clarify DENO_CERT behavior

[stil]

Can you please clarify the behavior of DENO_CERT env var?

docs/runtime/reference/env_variables.md

Line 68 in 8c523b8

| DENO_CERT | Load certificate authority from PEM encoded file |

I'm unsure what "loads" means here, does it append to the certs from DENO_TLS_CA_STORE or does it replace them?
How does it interact with DENO_TLS_CA_STORE, can both options be used at the same time or are they mutually exclusive?

Is behavior of DENO_CERT same as NODE_EXTRA_CA_CERTS where DENO_CERT is only for loading "extra" certificates?

Thank you