**- Why I did it**
To support dynamic buffer calculation.
This PR also depends on the following PRs for sub modules
- [sonic-swss: [buffermgr/bufferorch] Support dynamic buffer calculation #1338](https://github.com/Azure/sonic-swss/pull/1338)
- [sonic-swss-common: Dynamic buffer calculation #361](https://github.com/Azure/sonic-swss-common/pull/361)
- [sonic-utilities: Support dynamic buffer calculation #973](https://github.com/Azure/sonic-utilities/pull/973)
**- How I did it**
1. Introduce field `buffer_model` in `DEVICE_METADATA|localhost` to represent which buffer model is running in the system currently:
- `dynamic` for the dynamic buffer calculation model
- `traditional` for the traditional model in which the `pg_profile_lookup.ini` is used
2. Add the tables required for the feature:
- ASIC_TABLE in platform/\<vendor\>/asic_table.j2
- PERIPHERAL_TABLE in platform/\<vendor\>/peripheral_table.j2
- PORT_PERIPHERAL_TABLE on a per-platform basis in device/\<vendor\>/\<platform\>/port_peripheral_config.j2 for each platform with gearbox installed.
- DEFAULT_LOSSLESS_BUFFER_PARAMETER and LOSSLESS_TRAFFIC_PATTERN in files/build_templates/buffers_config.j2
- Add lossless PGs (3-4) for each port in files/build_templates/buffers_config.j2
3. Copy the newly introduced j2 files into the image and rendering them when the system starts
4. Update the CLI options for buffermgrd so that it can start with dynamic mode
5. Fetches the ASIC vendor name in orchagent:
- fetch the vendor name when creates the docker and pass it as a docker environment variable
- `buffermgrd` can use this passed-in variable
6. Clear buffer related tables from STATE_DB when swss docker starts
7. Update the src/sonic-config-engine/tests/sample_output/buffers-dell6100.json according to the buffer_config.j2
8. Remove buffer pool sizes for ingress pools and egress_lossy_pool
Update the buffer settings for dynamic buffer calculation
