Retrieve node key pair information using admin API

[chris-j-h]

• Add adminhost:port/config/keypairs endpoint to retrieve all key pairs for a particular node. Example response is:

[
   {
      "publicKey" : "oNspPPgszVUFw0qmGFfWwh1uxVUXgvBxleXORHj07g8="
   },
   {
      "publicKey" : "ABn6zhBth2qpdrJXp98IvjExV212ALl3j4U//nj4FAI="
   }
]

• Add adminhost:port/config/keypairs/{publickey} endpoint to check if node is registered with a particular key pair. Example response is:

  {
      "publicKey" : "oNspPPgszVUFw0qmGFfWwh1uxVUXgvBxleXORHj07g8="
   }

if the node is registered with the key pair, and:

No key pair found with public key oNspPPgszVUFw0qmGFfWwh1uxVUXgvBxleXORHj07g8=

if node is not registered with the key pair

[codecov-io]

Codecov Report

Merging #635 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master     #635      +/-   ##
============================================
+ Coverage     99.42%   99.43%   +<.01%     
- Complexity     1863     1869       +6     
============================================
  Files           289      290       +1     
  Lines          5782     5801      +19     
  Branches        273      274       +1     
============================================
+ Hits           5749     5768      +19     
  Misses            5        5              
  Partials         28       28

Impacted Files	Coverage Δ	Complexity Δ
.../java/com/quorum/tessera/admin/ConfigResource.java	100% <100%> (ø)	10 <3> (+3)	⬆️
.../quorum/tessera/core/config/ConfigServiceImpl.java	100% <100%> (ø)	7 <2> (+1)	⬆️
...va/com/quorum/tessera/admin/PublicKeyResponse.java	100% <100%> (ø)	2 <2> (?)

---

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