[swss] Restart countersyncd after unexpected exit

[Pterosaur]

Why I did it

Backport public SONiC PR sonic-net/sonic-buildimage#26147 to the 202412 branch.

swss:countersyncd in orchagent is started through dependent-startup, but the current supervisor stanza leaves it at EXITED after an unexpected exit instead of recovering it.

Work item tracking

• Microsoft ADO (number only): N/A

How I did it

• cherry-pick the original backport-safe changes from [swss] Restart countersyncd after unexpected exit sonic-net/sonic-buildimage#26147
• change countersyncd supervisor policy from autorestart=false to autorestart=unexpected
• set startsecs=10
• set startretries=3

How to verify it

Validated on 202412 DUT image 20241212.54.

Equivalent live-patched supervisor settings were applied on DUT str4-sn5640-2, then HFT telemetry validation was rerun successfully.

Relevant result:

• high_frequency_telemetry/test_high_frequency_telemetry.py::test_hft_port_counters
• result: 1 passed
• swss:countersyncd remained RUNNING after telemetry capture

Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006
• 202012
• 202106
• 202111
• 202205
• 202211
• 202305

Base branch of this PR is already 202412.

Tested branch (Please provide the tested image version)

• 20241212.54

Description for the changelog

Restart swss:countersyncd automatically after unexpected exits.

Link to config_db schema for YANG module changes

N/A

A picture of a cute animal (not mandatory but encouraged)

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