Is/routes admin api

[theotherian]

Still a few things left to work on, but I feel like I've been working on this so long I need to get some eyes on it.

To do:

• Add pagination to calls for collections of routes
• Add more JavaDoc
• Figure out proper boxed type when fetching all routes (probably shouldn't just load it all as instances of StaticRoute even if it's convenient)
• Add better handling of error cases in controller with Problems framework
• Expand controller test to ignore unknown fields? AccountSettingsSpringBootTest does this currently.

[codecov]

Codecov Report

Merging #406 into master will increase coverage by 2.51%.
The diff coverage is 64.6%.

@@             Coverage Diff              @@
##             master     #406      +/-   ##
============================================
+ Coverage     58.32%   60.84%   +2.51%     
- Complexity      741      804      +63     
============================================
  Files           236      247      +11     
  Lines          4533     4663     +130     
  Branches        173      179       +6     
============================================
+ Hits           2644     2837     +193     
+ Misses         1824     1755      -69     
- Partials         65       71       +6

Impacted Files	Coverage Δ	Complexity Δ
...dger/connector/settings/GlobalRoutingSettings.java	0% <ø> (ø)	0 <0> (ø)	⬇️
...ector/server/spring/controllers/PathConstants.java	0% <ø> (ø)	0 <0> (ø)	⬇️
.../java/org/interledger/connector/routing/Route.java	0% <ø> (ø)	0 <0> (ø)	⬇️
.../properties/ConnectorSettingsFromPropertyFile.java	86.56% <ø> (-0.76%)	15 <0> (ø)
.../connector/routing/StaticRouteNotFoundProblem.java	0% <0%> (ø)	0 <0> (?)
.../connector/routing/NoOpExternalRoutingService.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...rg/interledger/connector/routing/RoutingTable.java	0% <0%> (ø)	0 <0> (?)
...g/interledger/connector/DefaultILPv4Connector.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...org/interledger/connector/routing/StaticRoute.java	0% <0%> (ø)	0 <0> (?)
...ector/routing/StaticRouteUnprocessableProblem.java	0% <0%> (ø)	0 <0> (?)
... and 36 more

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[theotherian]

A few REST design questions spring to mind on this:

• I'm a subscriber to the philosophy that a GET on a collection resource that has no entities should just return a 200 with an empty collection rather than a 404. This is due to the fact that it's usually more arduous for the client to handle errors that don't represent a condition you're likely to fail on, and because I think it's a reasonable argument to say "there is an entity at this resource: it's an empty collection."
• While DELETE is guaranteed to be idempotent, you can communicate this two ways: either it always succeeds with some 2XX or only succeeds when something is deleted and returns a 404 otherwise. Usually I just do a 2XX but that's probably out of laziness. While you could argue that a 404 when missing is more specific, you also have the case that another client deleted it before you anyhow so it may not offer much helpful detail and may also make the job of the client more difficult.
• I'm opting to fail specifically on a constraint violation on the PUT rather than doing a prefetch. This is for 2 reasons: 1) a prefetch is vulnerable to race conditions and 2) in my case the PUT tolerates both create and update, meaning it's inaccurate to fail based merely on presence.

Curious if you have any strong feelings on any of these to the contrary.

[sappenin]

@theotherian apologies if some of my comments are redundant - I'm now seeing you thought of most of them in your PR comments.

[sappenin]

Minor nits from my side. If you want to merge as-is, we can address them in follow-ups or feel free to discuss here.

[sappenin]

@theotherian Great stuff in this PR, nice work!