Add helpers at /apis/{apiName}/listeners/{eventPath}

[awrichar]

This includes the commit from #693.

Add helper URLs:

GET /apis/{apiName}/listeners/{eventPath} - list all listeners matching this event on this API
POST /apis/{apiName}/listeners/{eventPath} - create a new listener for this event on this API

Also makes topic a required field for contract listeners, and enforces uniqueness of listeners across these 2 dimensions:

• namespace + name
• topic + contract location + event signature

Violating either uniqueness constraint when attempting to create a listener will result in HTTP 409, so applications can rely on this behavior to perform "create this listener if it does not already exist". Note that name is still optional, and a unique one will be assigned at creation time if none is specified.

[codecov-commenter]

Codecov Report

Merging #696 (87e5a23) into main (09a7cc6) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              main      #696    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files          323       323            
  Lines        19770     19874   +104     
==========================================
+ Hits         19770     19874   +104     

Impacted Files	Coverage Δ
pkg/fftypes/contract_listener.go	100.00% <ø> (ø)
pkg/fftypes/contracts.go	100.00% <ø> (ø)
...rnal/apiserver/route_get_contract_api_listeners.go	100.00% <100.00%> (ø)
internal/apiserver/route_get_contract_apis.go	100.00% <100.00%> (ø)
...nternal/apiserver/route_get_contract_interfaces.go	100.00% <100.00%> (ø)
...nal/apiserver/route_post_contract_api_listeners.go	100.00% <100.00%> (ø)
internal/blockchain/ethereum/ethereum.go	100.00% <100.00%> (ø)
internal/blockchain/fabric/fabric.go	100.00% <100.00%> (ø)
internal/contracts/manager.go	100.00% <100.00%> (ø)
...ternal/database/sqlcommon/contractlisteners_sql.go	100.00% <100.00%> (ø)
... and 3 more

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[peterbroadhurst]

Few questions from me here @awrichar

[peterbroadhurst]

Also, in the header comment of the PR (and soon in API descriptions fyi @nguyer ) would be good to note the 409 conflict behavior that allows apps the ability to do a create-if-not-exist check on startup with this great new API.

[peterbroadhurst]

👍