fix: implement filtering on cluster List API endpoint

[onematchfox]

For known security reasons, the Get endpoint on the Clusters service returns a 403 rather than a 404 if a cluster is not found. This means that in order to determine the non-existence of a cluster API, users need to make use of the List endpoint (see comment related to workaround on the behaviour on the applications service).

The application service implements filtering on List allowing the caller to effectively explicitly request a list consisting of a single application which makes this an effective workaround. However, at present, no form of filtering is applied on the cluster List API endpoint despite query parameters being available (see screenshot) below. This means that the same workaround for the clusters service is (extremely) inefficient as all clusters are returned on every call and the caller is left to iterate over all clusters. This PR addresses this issue by implementing filtering on this endpoint using the existing cluster query parameters (in the same manner as the application service.

Semi-related to #13000 (see comment here)

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[codecov]

Codecov Report

Patch coverage: 85.71% and project coverage change: +0.06 🎉

Comparison is base (67c254e) 49.17% compared to head (ef44e03) 49.24%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #13363      +/-   ##
==========================================
+ Coverage   49.17%   49.24%   +0.06%     
==========================================
  Files         248      248              
  Lines       42872    42925      +53     
==========================================
+ Hits        21084    21139      +55     
+ Misses      19687    19680       -7     
- Partials     2101     2106       +5     

Impacted Files	Coverage Δ
server/cluster/cluster.go	50.13% <85.71%> (+10.20%)	⬆️

... and 2 files with indirect coverage changes

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[ishitasequeira]

I tested the PR and the List call does work with the filer.

[crenshaw-dev]

@onematchfox would you mind adding a note to the 2.8 upgrade notes about this? Even though it's fixing something that's obviously broken, it is technically a breaking API change. Good to give folks a heads-up.

[onematchfox]

@onematchfox would you mind adding a note to the 2.8 upgrade notes about this? Even though it's fixing something that's obviously broken, it is technically a breaking API change. Good to give folks a heads-up.

@crenshaw-dev, not 100% sure what upgrade notes you are referring to - perhaps because I'm the first "upgrade note" for 2.8. Anyway, hopefully, what I've done is right.

[onematchfox]

@crenshaw-dev Just a reminder that this one is ready for final review

[crenshaw-dev]

Thanks, @onematchfox!