Replace straightforward sonic-cfggen calls with sonic-db-cli (#20232)

### Why I did it

Fix #20048

It is explained in ticket above, how sonic-cfggen calls in the hostname.sh, pcie-check.sh and banner-config and hogging the CPU and slightly delaying the start of swss

**pcie-check.sh**
redis-cli call is also replaced with sonic-db-cli since redis-cli is a wrapper around the actual redis-cli under database container
<img width="1113" alt="image" src="https://github.com/user-attachments/assets/bed9d055-3b9f-4f75-aabd-1e0335716396">

**swss start**
If the SKU has create_only_config_db_buffers.json set to true, the only config that's updated today is. 
```
{
    "DEVICE_METADATA": {
        "localhost": {
            "create_only_config_db_buffers": "true"
        }
    }
}
```
We use sonic-cfggen which cause 1.5 sec delay in the start of swss container. Thus replace with sonic-db-cli. If a complex use case arises in future, this can be updated.
<img width="1483" alt="Screenshot 2024-09-16 at 12 45 05 PM" src="https://github.com/user-attachments/assets/ee3248b5-7623-42c4-9b50-81b114c71ae7">


### How I did it

#### How to verify it

**Note: Everything was tested on MSN2700 device, Intel Celeron CPU with 2 cores**

- 1.5 sec saved in the swss container start
<img width="1298" alt="image" src="https://github.com/user-attachments/assets/817739f1-26a2-41ad-89e4-1e76e31532ac">

- 1.6 sec saved in the start of swss service. Previously, it took almost 1.8 sec after config-setup is finished for the swss to start. After replacing the calls, it start almost 0.2 sec after config-setup is finished

In total, anywhere between 2.5 - 3.5 sec is saved

files/build_templates/docker_image_ctl.j2

@@ -433,7 +433,7 @@ start() {
     if [ -d "$HWSKU_FOLDER" ]; then
         CREATE_ONLY_CONFIG_DB_BUFFERS_JSON="$HWSKU_FOLDER/create_only_config_db_buffers.json"
         if [ -f "$CREATE_ONLY_CONFIG_DB_BUFFERS_JSON" ]; then
-            $SONIC_CFGGEN -j $CREATE_ONLY_CONFIG_DB_BUFFERS_JSON --write-to-db
+            $SONIC_DB_CLI CONFIG_DB HSET 'DEVICE_METADATA|localhost' create_only_config_db_buffers true
         fi
     fi
     {%- endif %}

files/image_config/bannerconfig/banner-config.sh

@@ -1,14 +1,14 @@
 #!/bin/bash -e
 
-STATE=$(sonic-cfggen -d -v 'BANNER_MESSAGE["global"]["state"]')
+STATE=$(sonic-db-cli CONFIG_DB HGET 'BANNER_MESSAGE|global' state)
 LOGIN=
 MOTD=
 LOGOUT=
 
 if [[ $STATE == "enabled" ]]; then
-    LOGIN=$(sonic-cfggen -d -v 'BANNER_MESSAGE["global"]["login"]')
-    MOTD=$(sonic-cfggen -d -v 'BANNER_MESSAGE["global"]["motd"]')
-    LOGOUT=$(sonic-cfggen -d -v 'BANNER_MESSAGE["global"]["logout"]')
+    LOGIN=$(sonic-db-cli CONFIG_DB HGET 'BANNER_MESSAGE|global' login)
+    MOTD=$(sonic-db-cli CONFIG_DB HGET 'BANNER_MESSAGE|global' motd)
+    LOGOUT=$(sonic-db-cli CONFIG_DB HGET 'BANNER_MESSAGE|global' logout)
 
     echo -e "$LOGIN" > /etc/issue.net
     echo -e "$LOGIN" > /etc/issue

files/image_config/hostname/hostname-config.sh

@@ -1,7 +1,7 @@
 #!/bin/bash -e
 
-CURRENT_HOSTNAME=`hostname`
-HOSTNAME=`sonic-cfggen -d -v DEVICE_METADATA[\'localhost\'][\'hostname\']`
+CURRENT_HOSTNAME=$(hostname)
+HOSTNAME=$(sonic-db-cli CONFIG_DB HGET 'DEVICE_METADATA|localhost' hostname)
 
 if [ -z "$HOSTNAME" ] ; then
        echo "Missing hostname in the config file, setting to default 'sonic'"

files/image_config/pcie-check/pcie-check.sh

@@ -18,7 +18,7 @@ function debug()
 function check_and_rescan_pcie_devices()
 {
     PCIE_CHK_CMD='sudo pcieutil check | grep "$RESULTS"'
-    PLATFORM=$(sonic-cfggen -H -v DEVICE_METADATA.localhost.platform)
+    PLATFORM=$(sonic-db-cli CONFIG_DB HGET 'DEVICE_METADATA|localhost' platform)
 
     if [ ! -f /usr/share/sonic/device/$PLATFORM/pcie*.yaml ]; then
         debug "pcie.yaml does not exist! Can't check PCIe status!"
@@ -38,7 +38,7 @@ function check_and_rescan_pcie_devices()
         fi
 
         if [ "$(eval $PCIE_CHK_CMD)" = "$EXPECTED" ]; then
-            redis-cli -n 6 HSET $PCIE_STATUS_TABLE "status" "PASSED"
+            sonic-db-cli STATE_DB HSET $PCIE_STATUS_TABLE "status" "PASSED"
             debug "PCIe check passed"
             exit
         else
@@ -54,7 +54,7 @@ function check_and_rescan_pcie_devices()
 
      done
      debug "PCIe check failed"
-     redis-cli -n 6 HSET $PCIE_STATUS_TABLE "status" "FAILED"
+     sonic-db-cli STATE_DB HSET $PCIE_STATUS_TABLE "status" "FAILED"
 }
 
 check_and_rescan_pcie_devices

files/image_config/rsyslog/rsyslog-config.sh

@@ -1,6 +1,6 @@
 #!/bin/bash
 
-PLATFORM=`sonic-cfggen -H -v DEVICE_METADATA.localhost.platform`
+PLATFORM=$(sonic-db-cli CONFIG_DB HGET 'DEVICE_METADATA|localhost' platform)
 
 # Parse the device specific asic conf file, if it exists
 ASIC_CONF=/usr/share/sonic/device/$PLATFORM/asic.conf