implement NoTLS (--plaintext) support

[gertd]

This PR implements:

• topaz service support for running the gRPC services without TLS
• topaz CLI support for --plaintext

For the service part, when:

certs block entries contain empty string(s), like:

certs:
  tls_key_path: ''
  tls_cert_path: ''
  tls_ca_cert_path: ''

or
the certs block contains no entries like:

certs:

or
when no certs block is present

the gRPC service instance will start without the associated TLS credentials.

The topaz CLI add the --plaintext or -P parameter to indicate that the gRPC connection will use plain-text HTTP/2 when connecting to server (no TLS).

  -P, --plaintext                use plain-text HTTP/2 (no TLS) ($TOPAZ_PLAINTEXT)

When using grpcurl or grpcui use the -plaintext command line flag.

This PR also changes the default security mode of the health and metrics services to by default run with NoTLS.

[coveralls]

Pull Request Test Coverage Report for Build 11866052369

Details

• 36 of 532 (6.77%) changed or added relevant lines in 32 files are covered.
• 5 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.04%) to 8.495%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
cmd/topaz/main.go	0	1	0.0%
pkg/app/handlers/config.go	0	1	0.0%
pkg/cli/clients/directory/backup.go	0	1	0.0%
pkg/cli/clients/directory/export.go	0	1	0.0%
pkg/cli/cmd/cli.go	0	1	0.0%
pkg/cli/cmd/directory/backup.go	0	1	0.0%
pkg/cli/cmd/directory/exporter.go	0	1	0.0%
pkg/cli/cmd/directory/manifest.go	2	3	66.67%
pkg/cli/cmd/directory/restore.go	0	1	0.0%
pkg/cli/cmd/directory/stats.go	0	1	0.0%

Files with Coverage Reduction	New Missed Lines	%
pkg/debug/debug.go	1	0.0%
pkg/cc/config/config.go	1	0.0%
pkg/cc/config/loader.go	3	0.0%

Totals
Change from base Build 11788226662:	-0.04%
Covered Lines:	794
Relevant Lines:	9347

---

💛 - Coveralls

[carabasdaniel]

Overall looks good but if we move the service builder into internal, I think it might be possible to remove the service-host reference entirely