[8.3](backport #679) automate the ironbank docker context generation

[mergify]

This is an automatic backport of pull request #679 done by Mergify.

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[elasticmachine]

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• Start Time: 2022-07-20T10:57:42.404+0000

• Duration: 42 min 10 sec

Test stats 🧪

Test	Results
Failed	0
Passed	6089
Skipped	23
Total	6112

💚 Flaky test report

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[elasticmachine]

🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	97.222% (70/72)	👍
Files	68.326% (151/221)	👍
Classes	68.1% (301/442)	👍
Methods	51.722% (826/1597)	👍
Lines	38.008% (8851/23287)	👎 -0.039
Conditionals	100.0% (0/0)	💚

[v1v]

Test

➜  ea gsutil cp gs://fleet-ci-artifacts/elastic-agent/pull-requests/pr-751/elastic-agent-ironbank-8.3.3-SNAPSHOT-docker-build-context.tar.gz .
Copying gs://fleet-ci-artifacts/elastic-agent/pull-requests/pr-751/elastic-agent-ironbank-8.3.3-SNAPSHOT-docker-build-context.tar.gz...
/ [1 files][  9.3 KiB/  9.3 KiB]                                                
Operation completed over 1 objects/9.3 KiB.                                      
➜  ea tar xvf elastic-agent-ironbank-8.3.3-SNAPSHOT-docker-build-context.tar.gz 
x ./
x Dockerfile
x LICENSE
x README.md
x config
x config/docker-entrypoint
x hardening_manifest.yaml
➜  ea grep 8.3 *   
Dockerfile:ARG ELASTIC_STACK=8.3.3
README.md:Please follow the documentation on [Quick start](https://www.elastic.co/guide/en/fleet/8.3/fleet-elastic-agent-quick-start.html).
README.md:License](https://github.com/elastic/beats/blob/8.3/licenses/ELASTIC-LICENSE.txt),
README.md:[here](https://www.elastic.co/guide/en/beats/libbeat/current/release-notes-8.3.3.html).
grep: config: Is a directory
hardening_manifest.yaml:- "8.3.3"
hardening_manifest.yaml:  ELASTIC_STACK: "8.3.3"
hardening_manifest.yaml:  org.opencontainers.image.version: "8.3.3"
hardening_manifest.yaml:  - filename: "elastic-agent-8.3.3-linux-x86_64.tar.gz"
hardening_manifest.yaml:    url: "<artifact_path>/elastic-agent-8.3.3-linux-x86_64.tar.gz"