Allow overriding the JFrog CLI certificates directory

Is your feature request related to a problem? Please describe.
JFrog CLI currently loads custom CA certificates only from

$JFROG_CLI_HOME_DIR/security/certs

This makes the certificates directory dependent on the CLI home directory.

In some CI environments, JFROG_CLI_HOME_DIR is managed dynamically by the integration.
For example, the JFrog Jenkins Plugin creates a per-build CLI home under a path similar to:

$WORKSPACE_TMP/jfrog/<build-number>/.jfrog

This makes it difficult to provide centrally managed CA certificates, for example trough a Kubernetes secret mounted at fixed path.

Describe the solution you'd like to see
Add a new environment variable such as

JFROG_CLI_CERTS_DIR

When set, JFrog CLI should use this directory for custom CA certificates.

Describe alternatives you've considered

• Changing home dir path, but this is not always possible because CI integrations may override it.
• Adding the CA to the container's system trust store, but this is not practical when CI users provide their own container images
• Copying the CA into the dynamically created JFrog CLI home dir during build, which adds CI-specific workarounds and knowledge of the generated CLI home path.

Additional context
A seperate certificate direcory would be useful for:

• immutable container images
• centrally manged enterprise PKI
• Jenkins and other CI-system using temporary or per-build CLI home dirs.

No implementation files or tests are named in the issue. Start by locating the JFrog CLI code that loads custom CA certificates from $JFROG_CLI_HOME_DIR/security/certs, then trace its environment-variable handling; done means JFROG_CLI_CERTS_DIR selects an alternate certificate directory while the existing default still works, with coverage for both paths.