Reduce Ingester Allocations

[joe-elliott]

What this PR does:
Adds two new fields to tempopb.PushBytesRequest "traces" and "ids" and deprecated the "requests" field. traces are pre-marshalled byte slices containing trace which the ingester can now take directly to the wal without additional marshalling. Also added a TraceBytes object that the ingesters now write to the wal and eventually to the blocks.

Other changes:

• Many test improvements/additions
• Improve records check in append_block Find to prevent unnecessary lookups
• PushBytes supports both the old and new methods of pushing to the ingesters to recud
• Propagate context through instance.FindTraceByID()
• Added/extended functionality in the pkg/model package to support the new data encoding.
• Adjusted PreallocRequest to handle the new byte slices

Breaking Change!
Distributors will immediately attempt to start pushing to the ingesters with the new proto which will cause the new ingesters to silently ignore the new fields. To prevent any dropped spans roll out ingesters first and then distributors once all ingesters have upgraded.

Which issue(s) this PR fixes:
Fixes #658

Performance Before Changes
cpu usage seconds:

go gc duration seconds:

Performance After Changes
cpu usage seconds:

go gc duration seconds:

Checklist

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

[mdisibio]

Ran locally and stability and performance improvements all check out.