Healthcheck query publickey

[ptrus]

Healthcheck now also periodically tests querying public keys if the Oasis RPC API is enabled (which tests keymanager node access).

Renames metrics prefix from oasis_oasis_ to oasis_ (caused due the emerald-web3-gateway -> oasis_web3_gateway rename).

Fixes the oasis_ RPC endpoint to only be exposed if configured via ExposeOasisRPCs. Because the Public and Version fields in ethRPC.API were deprecated and not used, the endpoint was always exposed.

[codecov]

Codecov Report

Attention: 47 lines in your changes are missing coverage. Please review.

Comparison is base (1211f06) 62.42% compared to head (41dc50a) 61.08%.

❗ Current head 41dc50a differs from pull request most recent head 4fe0847. Consider uploading reports for the commit 4fe0847 to get more accurate results

Files	Patch %	Lines
rpc/oasis/health.go	0.00%	32 Missing ⚠️
rpc/apis.go	46.66%	7 Missing and 1 partial ⚠️
rpc/oasis/api.go	0.00%	6 Missing ⚠️
server/json_rpc.go	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #510      +/-   ##
==========================================
- Coverage   62.42%   61.08%   -1.35%     
==========================================
  Files          37       38       +1     
  Lines        3931     3962      +31     
==========================================
- Hits         2454     2420      -34     
- Misses       1272     1337      +65     
  Partials      205      205              

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