Upgrade node version to v18 in init scripts used by swagger pipeline (Azure#27606)

This is quick workaround before the swagger ci is upgraded to Node 18.

See [team's
discussion](https://teams.microsoft.com/l/message/19:[email protected]/1698761641017?tenantId=72f988bf-86f1-41af-91ab-2d7cd011db47&groupId=3e17dcb0-4257-4a30-b843-77f47f1d4121&parentMessageId=1698761641017&teamName=Azure%20SDK&channelName=Engineering%20System%20%F0%9F%9B%A0%EF%B8%8F&createdTime=1698761641017).

---------

Co-authored-by: Ray Chen <[email protected]>

Author: MaryGao

.scripts/automation_generate.sh

@@ -1,2 +1,5 @@
 #!/usr/bin/env bash
+export NVM_DIR="$HOME/.nvm"
+[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh" # This loads nvm
+nvm use default
 code-gen-pipeline --inputJsonPath=$1 --outputJsonPath=$2 --use=@autorest/typescript@^6.0.11 --typespecEmitter=@azure-tools/typespec-ts

.scripts/automation_init.sh

@@ -1,3 +1,8 @@
 #!/usr/bin/env bash
+curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.3/install.sh | bash
+export NVM_DIR="$HOME/.nvm"
+[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh" # This loads nvm
+nvm install v18.15.0 
+nvm alias default node
 npm install -g @microsoft/[email protected]
 npm install -g @azure-tools/js-sdk-release-tools