Reduce allocs in query path

[joe-elliott]

What this PR does:
Reduces allocs incurred by calling .Query() repeatedly. This method allocs a map under the hood. Benchmarks attached only address the frontend side of the improvements. The querier side would also be quite dramatic.

goos: darwin
goarch: arm64
pkg: github.com/grafana/tempo/modules/frontend
                  │  before.txt  │           after.txt           │
                  │    sec/op    │    sec/op     vs base         │
SearchPipeline-11   608.1m ± ∞ ¹   606.9m ± ∞ ¹  ~ (p=0.310 n=5)
¹ need >= 6 samples for confidence interval at level 0.95

                  │   before.txt   │              after.txt               │
                  │      B/op      │     B/op       vs base               │
SearchPipeline-11   10.645Mi ± ∞ ¹   9.149Mi ± ∞ ¹  -14.05% (p=0.008 n=5)
¹ need >= 6 samples for confidence interval at level 0.95

                  │  before.txt  │             after.txt              │
                  │  allocs/op   │  allocs/op    vs base              │
SearchPipeline-11   163.0k ± ∞ ¹   151.2k ± ∞ ¹  -7.24% (p=0.008 n=5)
¹ need >= 6 samples for confidence interval at level 0.95

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[ie-pham]

really cool PR 👍