Fix Jenkins image build; update Node; pin to serverless v3

[glin]

Fix Jenkins image build, currently failing because there was a new serverless major version v4 that requires Node >= 18:

 > [5/7] RUN npm install -g serverless:
5.776 /usr/local/bin/sls -> /usr/local/lib/node_modules/serverless/run.js
5.776 /usr/local/bin/serverless -> /usr/local/lib/node_modules/serverless/run.js
5.788 
5.788 > serverless@4.4.7 postinstall /usr/local/lib/node_modules/serverless
5.788 > node ./postInstall.js
5.788 
6.071 Error fetching release: EACCES: permission denied, open '/usr/local/lib/node_modules/serverless/node_modules/.bin/serverless-linux-amd64-0.0.2'
6.129 npm WARN notsup Unsupported engine for serverless@4.4.7: wanted: {"node":">=18.0.0"} (current: {"node":"14.21.3","npm":"6.14.18"})
6.129 npm WARN notsup Not compatible with your version of node/npm: serverless@4.4.7

• Update image to Node 22
• Run npm audit fix
• Pin to serverless v3, as serverless v4 apparently now requires a license