examples: add TLS support to basic price oracle service

[ffranr]

This commit adds basic TLS support to the example price oracle service. When connecting to the RPC price oracle, Tapd now assumes TLS. TLS certificate authentication is skipped by Tapd.

Simplify integration of the example price oracle with Tapd. (Hopefully helpful for @HannahMR )

[coveralls]

Pull Request Test Coverage Report for Build 11217147728

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 22 unchanged lines in 5 files lost coverage.
• Overall coverage increased (+0.001%) to 40.365%

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Files with Coverage Reduction	New Missed Lines	%
tappsbt/create.go	2	53.22%
commitment/tap.go	2	84.43%
asset/asset.go	2	81.61%
tapgarden/caretaker.go	4	68.5%
universe/interface.go	12	50.22%

Totals
Change from base Build 11131738711:	0.001%
Covered Lines:	24254
Relevant Lines:	60086

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💛 - Coveralls

[gijswijs]

LGTM! 🎉
I can still see some magic numbers in there, but that's expected for essentially a mock. But I just wanted to flag it.

Also, this server now only works with TLS. That's what we want, right?

Made a nit comment, but nothing that would block merging.

[ffranr]

Also, this server now only works with TLS. That's what we want, right?

@gijswijs yes, I think it will do for now. And tapd expects that right now.

[HannahMR]

This does solve the communication error between litd and the oracle in my testing.

[ffranr]

Also, this server now only works with TLS. That's what we want, right?

That's fine IMO. We just want to make sure that it can work with tapd out of the box.

[ffranr]

I've added logging to this and the format is sub-optimal. So I will improve before merge.

[Roasbeef]

LGTM 🐄