chore(dataobj): predicate pushdown metadata label filters

[ashwanthgoli]

What this PR does / why we need it:

Follow-up to #16802, adds support to build dataobj reader predicates from label filters that refer to structured metadata columns. This is done by looking up the metadata columns of each dataobj section and applying filters that refer to any of these columns, so the predicates and expressions for readers that operate on different sections on an object need not be the same.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Not part of this pr, but some though on applying stream filters: I think they can only be applied by looking at the labels of the matching streams for an object.
For streams containing the label, we can look at the value to either discard streams that do not match or discard the label filter from expression to avoid redundant work if there is a match

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR

[benclive]

Maybe pattern here too? That can add to the label set

[ashwanthgoli]

loki/pkg/logql/syntax/syntax.y.go

Lines 1371 to 1390 in 21bf5ee

	case 100:
	syntaxDollar = syntaxS[syntaxpt-1 : syntaxpt+1]
	{
	syntaxVAL.stage = newLabelParserExpr(OpParserTypeJSON, "")
	}
	case 101:
	syntaxDollar = syntaxS[syntaxpt-2 : syntaxpt+1]
	{
	syntaxVAL.stage = newLabelParserExpr(OpParserTypeRegexp, syntaxDollar[2].str)
	}
	case 102:
	syntaxDollar = syntaxS[syntaxpt-1 : syntaxpt+1]
	{
	syntaxVAL.stage = newLabelParserExpr(OpParserTypeUnpack, "")
	}
	case 103:
	syntaxDollar = syntaxS[syntaxpt-2 : syntaxpt+1]
	{
	syntaxVAL.stage = newLabelParserExpr(OpParserTypePattern, syntaxDollar[2].str)
	}

LineParserExpr should cover it