Relax version validation on generic packages

👕 Context

Generic packages versions are validated with this simple regex: /\A\d+\.\d+\.\d+\z/.

Users asked to be able to add labels similar to what is accepted in SemVer. Example: 1.0.0-rc. In addition, we received needs for simpler versions such as 1.2g and commit SHAs such as d50d836eb3de6177ce6c7a5482f27f9c2c84b672

See issues #273034 (closed), #325293 (closed) and #255234 (closed)

The package team decided to ease the validation of versions for generic packages.

🔬 What does this MR do?

• Update the package version validator for generic packages to use the maven_version
• Update the related specs
• Update the related documentation

🖼 Screenshots (strongly suggested)

Before this MR

$ curl --header "PRIVATE-TOKEN: XXXX" --upload-file ./dummy.txt "http://gdk.test:8000/api/v4/projects/71/packages/generic/my_package/1.2.2-rc/file.txt"
{"error":"package_version is invalid"}

With this MR

$ curl --header "PRIVATE-TOKEN: XXXX" --upload-file ./dummy.txt "http://gdk.test:8000/api/v4/projects/71/packages/generic/my_package/1.2.2-rc/file.txt"
{"message":"201 Created"}

🎉

📐 Does this MR meet the acceptance criteria?

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• [-] Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
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• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
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