feat(datasource/maven): Introduce option to assume that looked up maven data is specification compliant

[AB-xdev]

Changes

The current maven datasource lookup is not conform with the Maven standards and was only introduced because a few people used misconfigured maven repositories.

This PR introduces an experimental option RENOVATE_X_MAVEN_LOOKUP_ASSUME_SPECIFICATION_COMPLIANT.
If this is set, Renovate assumes that the looked up Maven Metadata conforms to specification and will skip some checks and requests.

Context

Fixes #27768

In the future it might be desirable to make this the default.

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[rarkins]

@zharinov is this partially redundant after your html changes?

[zharinov]

Oh yes, my final goal is to eliminate the need for option like this

[AB-xdev]

What changes are you talking about?

[philippe-granet]

What changes are you talking about?

#32662