[action] [PR:24188] [Arista] Use MEDIA_KEY and LANE_SPEED_KEY in media_settings.json file (#1724)

For x86_64-arista_7800r3a_36dm2_lc, use MEDIA_KEY and LANE_SPEED_KEY in media_settings.json to prevent OA crashes caused by speed misconfiguration.

#### Why I did it
Address https://github.com/aristanetworks/sonic-qual.msft/issues/876

##### Work item tracking
N/A

#### How I did it
Add LANE_SPEED_KEY to media_settings.json so that tuning values are selected based on the configured port speed. If the port speed is not supported by the inserted transceiver, the tuning value will be None and skipped, preventing it from being applied to the hardware. This avoids SAI call failures and, ultimately, OA crashes.

#### How to verify it
On a 7800r3a_36dm2 Linecard,
1. Tested 100G port with 400G optic; 'lane_speed_key' is None and tuning is skipped as there is NO matching key.
2025 Oct 2 05:31:04.377221 cmp235-3 NOTICE pmon#xcvrd: Retrieving media settings for port Ethernet96 speed 100000 num_lanes 4, using key {'vendor_key': 'ARISTA NETWORKS -AOC-D-D-400G-1M ', 'media_key': 'QSFP-DD-active_cable_media_interface', 'lane_speed_key': None, 'medium_lane_speed_key': 'COPPER25000'}

2. Tested a 400G port with 100G optic; Tuning is skipped because the lane_speed_key, 50G, do not match any keys in "Default" case.
2025 Oct 2 05:54:04.181472 cmp235-4 NOTICE pmon#xcvrd: Retrieving media settings for port Ethernet16 speed 400000 num_lanes 8, using key {'vendor_key': 'ARISTA NETWORKS -AOC-Q-Q-100G-1M ', 'media_key': 'QSFP28-100G AOC (Active Optical Cable) or 25GAUI C2M AOC-1.0M', 'lane_speed_key': 'speed:50G', 'medium_lane_speed_key': 'OPTICAL50000'}

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

- [ ] 202205
- [ ] 202211
- [ ] 202305
- [ ] 202311
- [x] 202405
- [ ] 202411
- [ ] 202505

#### Tested branch (Please provide the tested image version)
- [x] master
- [x] 202405

#### Description for the changelog
N/A

#### Link to config_db schema for YANG module changes
N/A

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

Author: mssonicbld