[Snyk] Security upgrade ubuntu from latest to 22.04

[snyk-bot]

Keeping your Docker base image up-to-date means you’ll benefit from security fixes in the latest version of your chosen image.

Changes included in this PR

• docs/examples/postgresql_service.Dockerfile

We recommend upgrading to ubuntu:22.04, as this image has only 8 known vulnerabilities. To do this, merge this pull request, then verify your application still works as expected.

Some of the most important vulnerabilities in your base image include:

Severity	Priority Score / 1000	Issue	Exploit Maturity
	221	NULL Pointer Dereference SNYK-UBUNTU2204-OPENSSL-3043317	No Known Exploit
	****	Improper Verification of Cryptographic Signature SNYK-UBUNTU2204-PERL-2789081	No Known Exploit
	150	Time-of-check Time-of-use (TOCTOU) SNYK-UBUNTU2204-SHADOW-2801886	No Known Exploit
	150	Time-of-check Time-of-use (TOCTOU) SNYK-UBUNTU2204-SHADOW-2801886	No Known Exploit
	****	Out-of-bounds Write SNYK-UBUNTU2204-ZLIB-2975633	No Known Exploit

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