Enhance integration tests for SSL/TLS scenarios

[jportner]

We don't currently have optimal coverage for various SSL/TLS scenarios with our current integration tests. We added some in #53810, but this gap is exacerbated now that we support loading certificates/keys from PKCS#12 keystores. We should do the following:

1. Refactor existing integration tests to use Jest integration tests
2. Add extra tests to increase our coverage

Various permutations of scenarios are:

[Kibana | Elasticsearch] HTTP connection, testing [client cert authentication | server cert trust] using [PEM | PKCS12]-formatted cert, signed by [root CA | intermediate CA]

We should test the success and failure cases of each of these scenarios.

We should also test different types of certs including:

• Combinations of SAN and CN, with different values (IP address, FQDN)
• Attributes (such as CA:FALSE/CA:TRUE and others)
• Key types (RSA, ECC)

We should also change our tests to dynamically generate certificates instead of using hard-coded certs. https://github.com/MatthiasValvekens/certomancer might be a good tool to use for this.

[elasticmachine]

Pinging @elastic/kibana-security (Team:Security)