Include computer name in AgentRegistration & decode Instance ID from it

[Porges]

Addressing #2550 but in a slightly different way:

1. Always include the machine name in the agent registration message. From the machine name we can extract the instance ID.
2. Use the stored value in preference to fetching it every time.
3. To back-fill existing nodes that do not have the value stored, update it in AcquireScaleInProtection if it is not already present.

[mgreisen]

@Porges I just remembered the work that @chkeita is doing with unmanaged nodes. Unmanaged nodes are likely to have some other naming scheme. I'm not sure how we will distinguish when registering.

[codecov-commenter]

Codecov Report

Merging #2557 (c628f87) into main (0e8876b) will decrease coverage by 5.69%.
The diff coverage is 13.04%.

@@            Coverage Diff             @@
##             main    #2557      +/-   ##
==========================================
- Coverage   35.52%   29.83%   -5.70%     
==========================================
  Files         134      289     +155     
  Lines       17123    35747   +18624     
==========================================
+ Hits         6083    10664    +4581     
- Misses      11040    25083   +14043     

Impacted Files	Coverage Δ
...piService/ApiService/Functions/AgentCanSchedule.cs	0.00% <0.00%> (ø)
...c/ApiService/ApiService/TestHooks/VmssTestHooks.cs	0.00% <0.00%> (ø)
...ApiService/ApiService/onefuzzlib/NodeOperations.cs	23.65% <0.00%> (ø)
...ApiService/ApiService/onefuzzlib/VmssOperations.cs	0.00% <0.00%> (ø)
src/agent/onefuzz-agent/src/config.rs	0.00% <0.00%> (ø)
...iService/ApiService/Functions/AgentRegistration.cs	89.71% <66.66%> (ø)
src/ApiService/ApiService/OneFuzzTypes/Model.cs	71.97% <100.00%> (ø)
...rc/ApiService/ApiService/onefuzzlib/InstanceIds.cs	100.00% <100.00%> (ø)
src/agent/input-tester/src/lib.rs	2.94% <0.00%> (-97.06%)	⬇️
src/agent/win-util/src/lib.rs	18.51% <0.00%> (-81.49%)	⬇️
... and 174 more

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[Porges]

@Porges I just remembered the work that @chkeita is doing with unmanaged nodes. Unmanaged nodes are likely to have some other naming scheme. I'm not sure how we will distinguish when registering.

Yes, we will have to have different handling for them. If they send null for this then we would fall back to the existing code path. We are going to have to have different handling for unmanaged nodes in any case, so I don’t think this change will adversely affect that work.