Make self-send check more robust

[prd-fox]

In certain cases, such as a misconfigured network, it is possible we think we are sending to ourselves but are infact not, based on the URL of the recipient. See issue #546 as an example.

Instead, the proper way of checking if we are sending to ourselves would be to check if the public key we are sending to is one of the keys that our own enclave manages.

In the case that the target URL is the same as ours, then the call will still go ahead and print what the target is (to identify misconfigured networks more easily).

[codecov-io]

Codecov Report

Merging #571 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master     #571      +/-   ##
============================================
+ Coverage     99.49%   99.51%   +0.02%     
  Complexity     1481     1481              
============================================
  Files           238      238              
  Lines          4546     4547       +1     
  Branches        227      226       -1     
============================================
+ Hits           4523     4525       +2     
  Misses            2        2              
+ Partials         21       20       -1

Impacted Files	Coverage Δ	Complexity Δ
...orum/tessera/transaction/PayloadPublisherImpl.java	100% <100%> (+4.16%)	4 <3> (ø)	⬇️

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