chore: update release issue template

[czeslavo]

What this PR does / why we need it:

As a follow-up to #3199:

• merge docs steps into one
• add details for FOSSA report generate
• add a step for ensuring the latest Gateway image is used in manifests

Which issue this PR fixes:

Part of https://github.com/Kong/team-k8s/issues/267.

[codecov]

Codecov Report

Base: 74.0% // Head: 74.0% // Increases project coverage by +0.0% 🎉

Coverage data is based on head (462a5cd) compared to base (4ed3ad5).
Patch has no changes to coverable lines.

❗ Current head 462a5cd differs from pull request most recent head 726d2cd. Consider uploading reports for the commit 726d2cd to get more accurate results

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #3294   +/-   ##
=====================================
  Coverage   74.0%   74.0%           
=====================================
  Files        111     111           
  Lines      13285   13285           
=====================================
+ Hits        9843    9844    +1     
+ Misses      2816    2814    -2     
- Partials     626     627    +1     

Impacted Files	Coverage Δ
...nternal/controllers/gateway/tcproute_controller.go	73.0% <0.0%> (-2.7%)	⬇️
...ternal/controllers/gateway/httproute_controller.go	54.2% <0.0%> (-1.7%)	⬇️
internal/dataplane/parser/parser.go	90.7% <0.0%> (+1.0%)	⬆️
internal/dataplane/kongstate/kongstate.go	70.5% <0.0%> (+1.1%)	⬆️
...nternal/controllers/gateway/tlsroute_controller.go	75.8% <0.0%> (+2.6%)	⬆️

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