Make all search case-sensitive

[mdisibio]

Tempo currently has different case sensitivity when searching different data: recent traces (ingesters) is case-insensitive, while backend blocks are case-sensitive. This is not intentional and leads to inconsistent search results, even the same query can give different results over time as a trace moves from the ingesters to the backend.

The consensus is that case-sensitive is the better approach. This also includes the autocomplete lookups, for tags and tag values. They currently always lower-case, and they should preserve the original case.