ci: prime GitHub cache with Docker images built on main

[rjaegers]

GitHub cache can re-use cached data from ancestor branches. This PR adds a Docker build for all supported platforms on main that primes the cache. This should speed-up builds on feature branches and on the merge queue.

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ ACTION	actionlint	11		0	0.02s
✅ DOCKERFILE	hadolint	1		0	0.32s
✅ JSON	eslint-plugin-jsonc	7	0	0	4.69s
✅ JSON	prettier	7	0	0	0.45s
✅ JSON	v8r	7		0	3.58s
✅ MARKDOWN	markdownlint	3	0	0	0.88s
✅ MARKDOWN	markdown-link-check	3		0	3.28s
✅ MARKDOWN	markdown-table-formatter	3	0	0	0.24s
✅ REPOSITORY	checkov	yes		no	17.2s
✅ REPOSITORY	dustilock	yes		no	0.12s
✅ REPOSITORY	gitleaks	yes		no	0.25s
✅ REPOSITORY	git_diff	yes		no	0.0s
✅ REPOSITORY	grype	yes		no	12.61s
✅ REPOSITORY	secretlint	yes		no	1.27s
✅ REPOSITORY	syft	yes		no	0.73s
✅ REPOSITORY	trivy	yes		no	6.93s
✅ REPOSITORY	trivy-sbom	yes		no	3.47s
✅ REPOSITORY	trufflehog	yes		no	4.88s
✅ SPELL	lychee	32		0	0.73s
✅ YAML	prettier	13	0	0	0.78s
✅ YAML	v8r	13		0	10.83s
✅ YAML	yamllint	13		0	1.18s

See detailed report in MegaLinter reports

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[github-actions]

Test Results

16 tests  ±0   16 ✔️ ±0   34s ⏱️ -2s
  1 suites ±0     0 💤 ±0 
  1 files   ±0     0 ❌ ±0 

Results for commit 497a660. ± Comparison against base commit 55d2f39.

[github-actions]

Pull Request Report (#198)

Static measures

Description	Value
Number of added lines	26
Number of deleted lines	0
Number of changed files	1
Number of commits	3
Number of reviews	1
Number of comments (w/o review comments)	2
Number of reviews that contains a comment to resolve	0
Number of reviews that requested a change from the author	0
Number of reviews that approved the Pull Request	1
Get the total number of participants of a Pull Request	3

Time related measures

Description	Value
PR lead time (from creation to close of PR)	4 Hours
Time that was spend on the branch before the PR was created	2.4 Min
Time that was spend on the branch before the PR was merged	4.1 Hours
Time to merge after last review	2.8 Hours

Status check related measures

Description	Value
Total runtime for last status check run (Workflow for PR)	1.4 Hours
Total time spend in last status check run on PR	59.4 Min