[portsorch] Ports initialization speedup

[stepanblyschak]

DEPENDS ON: sonic-net/sonic-sairedis#1509

What I did

Optimized port initialization process using the following approach:

1. Attributes that are known at initialization (whether because their default values are defined by the SAI spec or because we created the port with a value we already know) like speed and MTU.
2. Heavy operations like querying list of PGs and queues are done in bulk to save on SAIRedis call overhead.
3. Port initialization that has no dependncy on subsequent data plane configuration are extracted into a seperate "post initialization" routine and executed after data plane configuration is done.
4. Save SAI set API call when possible to provide a value during creation.

Why I did it

To improve boot time for systems with many ports.

How I verified it

Ran fast-reboot and measure. Observed 45% reduction in time.

Details if related

[mssonicbld]

/azp run

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[mssonicbld]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).