[DO NOT MERGE] attribute: add BYTES type support

[NesterovYehor]

Caution

This should not be merged before we have a v1.41.0 release.

Fixes #7933

Add BYTES type to https://pkg.go.dev/go.opentelemetry.io/otel/attribute

• Introduces BYTES type and byte
• Adds Bytes / BytesValue constructors
• Implements hashing support
• Adds base64 representation in Emit()
• Adds test coverage for constructors, hashing, and set equality

$  go test -run=^$ -bench='BenchmarkBytesValue|BenchmarkAsBytes' -benchmem
goos: darwin
goarch: arm64
pkg: go.opentelemetry.io/otel/attribute/internal
cpu: Apple M1
BenchmarkBytesValue-8   	17996593	        66.35 ns/op	       6 B/op	       2 allocs/op
BenchmarkAsBytes-8      	47359774	        26.59 ns/op	       2 B/op	       1 allocs/op
PASS
ok  	go.opentelemetry.io/otel/attribute/internal	2.995s

$  go test -run=^$ -bench=BenchmarkBytes -benchmem
goos: darwin
goarch: arm64
pkg: go.opentelemetry.io/otel/attribute
cpu: Apple M1
BenchmarkBytes/Value-8         	15589729	        69.47 ns/op	      32 B/op	       2 allocs/op
BenchmarkBytes/KeyValue-8      	16409461	        80.14 ns/op	      32 B/op	       2 allocs/op
BenchmarkBytes/AsBytes-8       	40278198	        29.09 ns/op	      16 B/op	       1 allocs/op
BenchmarkBytes/Emit-8          	22664637	        51.59 ns/op	      32 B/op	       2 allocs/op
PASS
ok  	go.opentelemetry.io/otel/attribute	5.180s

[codecov]

Codecov Report

❌ Patch coverage is 86.84211% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.7%. Comparing base (248da95) to head (95b2ce9).

Files with missing lines	Patch %	Lines
log/keyvalue.go	0.0%	3 Missing ⚠️
attribute/internal/attribute.go	83.3%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #7948   +/-   ##
=====================================
  Coverage   81.7%   81.7%           
=====================================
  Files        304     304           
  Lines      23287   23325   +38     
=====================================
+ Hits       19039   19074   +35     
- Misses      3862    3865    +3     
  Partials     386     386           

Files with missing lines	Coverage Δ
attribute/hash.go	90.1% <100.0%> (+1.0%)	⬆️
attribute/key.go	100.0% <100.0%> (ø)
attribute/kv.go	100.0% <100.0%> (ø)
attribute/type_string.go	60.0% <ø> (ø)
attribute/value.go	93.2% <100.0%> (+0.6%)	⬆️
attribute/internal/attribute.go	83.3% <83.3%> (ø)
log/keyvalue.go	95.6% <0.0%> (-1.5%)	⬇️

... and 1 file with indirect coverage changes

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[pellared]

Overall LGTM. I left a few comments.
Please also add the benchmark results for ``BenchmarkBytes` in the PR description.

[pellared]

@NesterovYehor

We would also need to comply with SDK attribute value limits https://opentelemetry.io/docs/specs/otel/common/#anyvalue

if it is a byte array, if its length exceeds that limit (counting each byte as 1), SDKs MUST truncate that value, so that its length is at most equal to the limit,

I propose to do this in a separate PR and also track it in a separate issue. The important thing is that both PRs would need to be shipped in the same release. If you want you can already start working it in a separate branch / draft PR

EDIT: I created #7954