Add Aggregation Storage

[lalitb]

Fixes #1197 #1202

Changes

As discussed in today's community meeting, this PR adds the first part of Aggregation Storage - to consume/record the measurements and store them against the Aggregation objects. To achieve thread-safe aggregation storage, we use a non-blocking mutex lock SpinLockMutex. The benchmark tests are added, and will continue to look into lock-free concurrent storage libraries in C++ ( similar to [ConcurrentHashMap ](https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentHashMap.html in java ) which provides lock free retrievals. Some of the available options to look into:

1. Atomic Unordered map from Facebook - https://github.com/facebook/folly/blob/main/folly/AtomicUnorderedMap.h
2. Intel thread building blocks - https://github.com/oneapi-src/oneTBB

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #1213 (7b9fb31) into main (15c6f33) will decrease coverage by 0.37%.
The diff coverage is 77.24%.

@@            Coverage Diff             @@
##             main    #1213      +/-   ##
==========================================
- Coverage   93.35%   92.99%   -0.36%     
==========================================
  Files         193      196       +3     
  Lines        6908     7038     +130     
==========================================
+ Hits         6448     6544      +96     
- Misses        460      494      +34     

Impacted Files	Coverage Δ
.../opentelemetry/sdk/metrics/measurement_processor.h	40.00% <0.00%> (-2.10%)	⬇️
...ntelemetry/sdk/metrics/state/sync_metric_storage.h	52.95% <48.94%> (-1.60%)	⬇️
...entelemetry/sdk/metrics/state/attributes_hashmap.h	93.94% <93.94%> (ø)
sdk/test/metrics/attributes_hashmap_test.cc	100.00% <100.00%> (ø)
sdk/test/metrics/sync_metric_storage_test.cc	100.00% <100.00%> (ø)
...etry/sdk/metrics/aggregation/default_aggregation.h	0.00% <0.00%> (ø)
...ntelemetry/sdk/metrics/view/attributes_processor.h	100.00% <0.00%> (+18.75%)	⬆️
...lemetry/sdk/metrics/aggregation/drop_aggregation.h	50.00% <0.00%> (+25.00%)	⬆️

[esigo]

LGTM
Thanks for the PR :)