attribute: add BYTES type support

[NesterovYehor]

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 93.02326% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.7%. Comparing base (5c12b73) to head (93e1f96).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
log/keyvalue.go	78.5%	3 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #7948   +/-   ##
=====================================
  Coverage   81.7%   81.7%           
=====================================
  Files        308     308           
  Lines      23655   23681   +26     
=====================================
+ Hits       19343   19365   +22     
- Misses      3930    3933    +3     
- Partials     382     383    +1     

Files with missing lines	Coverage Δ
attribute/hash.go	92.0% <100.0%> (+0.5%)	⬆️
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	92.6% <100.0%> (+0.7%)	⬆️
...otlp/otlplog/otlploggrpc/internal/transform/log.go	96.1% <100.0%> (ø)
...otlp/otlplog/otlploghttp/internal/transform/log.go	96.1% <100.0%> (ø)
exporters/stdout/stdoutlog/record.go	96.9% <100.0%> (ø)
log/kind_string.go	60.0% <ø> (ø)
log/keyvalue.go	95.6% <78.5%> (-1.5%)	⬇️

... and 2 files 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

[pellared]

@open-telemetry/go-approvers, PTAL. This can be now merged given the recent releases.

[MrAlias]

Overall looks good. The hashing algorithm access needs attention though.

[pellared]

Can you please add support for BYTES in the OTLP exporters?
This can be done in a separate PR like #7990.

[dashpole]

LGTM after @MrAlias's comments are addressed.

[MrAlias]

Blocking base on #7948 (comment)

Investigation needs to be undertaken to storing the []byte as a string in value instead as a slice.