- Upstream release (and use the supplied config file instead of keeping a copy).
- Switch to fully locked system account

Switch nodejs-lts from -hydrogen to -iron

Fix license, it was changed in https://framagit.org/kresusapp/kresus/-/commit/e9bb809425df439a5e86fb8896a9262a69bea3f0
Also use SPDX identifier while at it

from npm. 

AF_NETLINK is now required by node, else it errors with:

node:os:68
      throw new ERR_SYSTEM_ERROR(ctx);
      ^
SystemError [ERR_SYSTEM_ERROR]: A system error occurred: uv_interface_addresses returned Unknown system error 97 (Unknown system error 97)
    at Object.networkInterfaces (node:os:259:16)
    at Object.<anonymous> (/usr/lib/kresus/node_modules/nodemailer/lib/shared/index.js:15:66)
    at Module._compile (node:internal/modules/cjs/loader:1105:14)
    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1159:10)
    at Module.load (node:internal/modules/cjs/loader:981:32)
    at Function.Module._load (node:internal/modules/cjs/loader:822:12)
    at Module.require (node:internal/modules/cjs/loader:1005:19)
    at require (node:internal/modules/cjs/helpers:102:18)
    at Object.<anonymous> (/usr/lib/kresus/node_modules/nodemailer/lib/mailer/index.js:4:16)
    at Module._compile (node:internal/modules/cjs/loader:1105:14) {
  code: 'ERR_SYSTEM_ERROR',
  info: {
    errno: 97,
    code: 'Unknown system error 97',
    message: 'Unknown system error 97',
    syscall: 'uv_interface_addresses'
  },
  errno: [Getter/Setter],
  syscall: [Getter/Setter]
}

They are incompatibilities with 12.x

Also harden even more.