Release v0.9.0

Summary of Changes

• .github/workflows: build windows binaries in cross-build stage (#509, @tklauser)
• Add a flag to disable the ipcache check (#503, @michi-covalent)
• add hubble-ui status (#478, @zhaojizhuang)
• Add managed endpoint count to status command (#499, @zhaojizhuang)
• Add support for displaying the running Cilium version (#482, @zhaojizhuang)
• Add Windows executable to release (#488, @tklauser)
• all: convert to SPDX license headers (#496, @tklauser)
• build(deps): bump 8398a7/action-slack from 3.9.1 to 3.9.2 (#487, @dependabot[bot])
• build(deps): bump actions/upload-artifact from 2.2.3 to 2.2.4 (#475, @dependabot[bot])
• build(deps): bump aws-actions/configure-aws-credentials from 1.5.10 to 1.5.11 (#497, @dependabot[bot])
• build(deps): bump docker/build-push-action from 2.5.0 to 2.6.1 (#446, @dependabot[bot])
• build(deps): bump docker/build-push-action from 2.6.1 to 2.7.0 (#502, @dependabot[bot])
• Bump k8s dependencies to 1.21.4 (#486, @tklauser)
• ci: bump golangci-lint to v1.42.0 (#493, @tklauser)
• connectivity: use the right test namespace in cnps (#330, @bmcustodio)
• external workload: Increase the VM creation retry count (#473, @michi-covalent)
• Fix make release target (#523, @tklauser)
• Fix flow validation breakage (#485, @jrajahalme)
• go.mod, vendor: bump github.com/go-openapi/strfmt to v0.20.2 (#501, @tklauser)
• go.mod, vendor: bump github.com/ulikunitz/xz to v0.5.10 to fix GHSA-25xm-hr59-7c27 (#500, @tklauser)
• install: set base version to current default version (#504, @tklauser)
• internal/cli/cmd: fix formatting linter issue (#483, @tklauser)
• internal/cli/cmd: mark --skip-ip-cache-check as hidden (#508, @tklauser)
• k8s: Use TTY to cancel execution (#443, @jrajahalme)
• main: Add gops agent (#325, @jrajahalme)
• More release process fixes (#525, @tklauser)
• Prepare for release v0.8.6 (#468, @michi-covalent)
• Simplify the release process a bit (#469, @michi-covalent)
• Switch pod to world testing from cilium.io to one.one.one.one (#511, @nbusseneau)
• sysdump: collect 'clustermesh-apiserver' + improvements (#513, @bmcustodio)
• sysdump: Remove the Hidden flag (#481, @michi-covalent)
• Test failure output improvements (#316, @jrajahalme)
• test: Add error detail to ipcache check failures (#444, @jrajahalme)
• test: validate exit code and add HTTP drop testing (#318, @jrajahalme)
• test: Validate Service IP (#422, @jrajahalme)
• Update Cilium to v1.10.4 (#516, @tklauser)
• Update Go to 1.16.7 (#476, @tklauser)
• Update Go to 1.17 (#494, @tklauser)
• use default/kubernetes to test for dns (#479, @zhaojizhuang)