[bugfix] Resolve lost reference to meta object in ResultMetricCollection

[tchaton]

What does this PR do?

This PR resolves a bug where the meta object was lost during ResultCollection.to function.

I removed entirely the usage of Metadata through the init function as this was definitely a wrong pattern.

Now, the meta object is resolved directly from the children.

Fixes #8918

Does your PR introduce any breaking changes? If yes, please list them.

No.

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[codecov]

Codecov Report

Merging #8932 (6da0be1) into master (93ab24d) will increase coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #8932   +/-   ##
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  Coverage      93%     93%           
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  Files         172     172           
  Lines       14096   14096           
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+ Hits        13098   13099    +1     
+ Misses        998     997    -1