feat: add HTML response handling for job and target endpoints

[CharlieTLe]

Description:
Adds support for HTML output in the target allocator.

Link to tracking Issue(s):

• Resolves: UI for Jobs and Scrape Configs in Target Allocator Server #3622

Testing:
End to end testing with chainsaw allows for inspecting the Target Allocator's HTML output.

To start the test, run

make prepare-e2e && ./bin/chainsaw test tests/e2e-targetallocator/targetallocator-prometheuscr/ --cleanup-delay 300s

Once the chainsaw tests starts, port-forward to the TA pod.

ns=$(k get deploy -A -l app.kubernetes.io/component=opentelemetry-targetallocator -o json | jq -r '.items[0].metadata.namespace') && k port-forward -n $ns deploy/prometheus-cr-targetallocator 8080:8080

Once port-forwarded, go to http://localhost:8080.

Documentation: