feat: add support to supply a CA cert for untrusted CA certs

[splicemaahs]

Description

Provide a mechanism to supply a CA certificate to use in validation of the SSL endpoint for splicectl-api. This allows use of self-signed certs or certs that are signed by an untrusted CA.

The primary work is done in main.go. Reading from --cacert and SPLICECTL_CACERT. The rest of the edits are all the same, consuming the caBundle set in main.go and passing it to the goresty object.

Motivation and Context

In many on-prem installation we may not have a CA issued for POC and need a way to handle self-signed certificates.

Dependencies

How Has This Been Tested?

The functionality remains exactly the same if --cacert or export SPLICECTL_CACERT= are not specified or set.

Screenshots (if appropriate)

Checklist

If the pull request includes user-facing changes, extra documentation is required:

• If the change is user facing, please ensure you add info in one of the Changelog Inclusions sections.

Changelog Inclusions

Additions

• added --cacert /path/to/cert.crt to pass in a certificate used as the CA to validate SSL connections
• added support to read from SPLICECTL_CACERT=/path/to/cert.crt to auto-set the --cacert option.

Changes

Fixes

Deprecated

Removed

Breaking Changes