Allow setting of Consul ServiceMeta tags from config file

[unRob]

Hi there!

I'd love to be able to set ServiceMeta on the Consul service registered by Vault by specifying the desired tags in the config file, and I'm submitting this PR to that effect.

I'm not happy about unmarshalling json during NewServiceRegistration but considered that a simpler change than the couple of alternatives I came up from a quick glance at the codebase. That is to say, I'd love feedback on the approach (and perhaps suggestions on a proper testing strategy should folks feel this approach works).

fixes #9121 see also #10233

[hashicorp-cla]

All committers have signed the CLA.

[unRob]

Still very interested in seeing this through, any chance it could be reviewed?