[pmon] create and mount firmware directory on PMON for firmware upgra…

…de support on muxcable (#8283)

This PR creates a directory firmware on the HOST with the path /usr/share/sonic/firmware, as well as this is 
mounted on PMON container with the same path /usr/share/sonic/firmware. This is required for firmware 
upgrade support for muxcable as currently by design all Y-Cable API's are called by xcvrd. As such if CLI has 
to transfer a file to PMON we need to mount a directory from host to PMON just for getting the firmware files. 
Hence we require this change.

Signed-off-by: vaibhav-dahiya <vdahiya@microsoft.com>

files/build_templates/docker_image_ctl.j2

@@ -374,6 +374,9 @@ start() {
         -v /var/run/docker-syncd$DEV:/var/run/sswsyncd \
 {%- endif %}
 {%- endif %}
+{%- if docker_container_name == "pmon" %}
+    -v /usr/share/sonic/firmware:/usr/share/sonic/firmware:rw \
+{%- endif %}
 {%- if docker_container_name == "swss" %}
         -e ASIC_VENDOR=$ASIC_VENDOR \
 {%- endif -%}

files/build_templates/sonic_debian_extension.j2

@@ -45,6 +45,7 @@ FILESYSTEM_ROOT_USR_SHARE="$FILESYSTEM_ROOT_USR/share"
 FILESYSTEM_ROOT_USR_SHARE_SONIC="$FILESYSTEM_ROOT_USR_SHARE/sonic"
 FILESYSTEM_ROOT_USR_SHARE_SONIC_SCRIPTS="$FILESYSTEM_ROOT_USR_SHARE_SONIC/scripts"
 FILESYSTEM_ROOT_USR_SHARE_SONIC_TEMPLATES="$FILESYSTEM_ROOT_USR_SHARE_SONIC/templates"
+FILESYSTEM_ROOT_USR_SHARE_SONIC_FIRMWARE="$FILESYSTEM_ROOT_USR_SHARE_SONIC/firmware"
 FILESYSTEM_ROOT_ETC="$FILESYSTEM_ROOT/etc"
 FILESYSTEM_ROOT_ETC_SONIC="$FILESYSTEM_ROOT_ETC/sonic"
 
@@ -85,6 +86,7 @@ sudo mkdir -p $FILESYSTEM_ROOT/etc/sonic/
 sudo mkdir -p $FILESYSTEM_ROOT/etc/modprobe.d/
 sudo mkdir -p $FILESYSTEM_ROOT/var/cache/sonic/
 sudo mkdir -p $FILESYSTEM_ROOT_USR_SHARE_SONIC_TEMPLATES/
+sudo mkdir -p $FILESYSTEM_ROOT_USR_SHARE_SONIC_FIRMWARE/
 # This is needed for Stretch and might not be needed for Buster where Linux create this directory by default.
 # Keeping it generic. It should not harm anyways.
 sudo mkdir -p $FILESYSTEM_ROOT_USR_LIB_SYSTEMD_SYSTEM