Add optional insecure flag for self-signed certificates in script

[Boubik]

Add support for insecure flag in installation script

Add optional --insecure. Pass -insecure to rmmagent for both initial install and the systemd service (ExecStart). Add --no-check-certificate to wget when fetching MeshAgent. Update help output to document the flag.

Example:

./rmmagent-linux.sh install "<mesh_url>" "<api_url>" <client_id> <site_id> "<auth_key>" server --insecure Omit --insecure to retain default secure behavior.

Compatibility

Backwards compatible: default behavior unchanged when the flag is not supplied.

##Testing

Verified install with and without --insecure. Confirmed: self-signed cert scenarios no longer block API enrollment or MeshAgent download. Confirmed: rerunning installer no longer errors on existing mesh directory or missing temp files.