Regex for string starting with doueble quote and ending with [ - json

Question

I have to update dictionary with new value for existing key in a JSON file.
I need no write new line after existing string using regex
Current file:
{
"id": "aaaa",
"desc": "Service aaa",
"boss":"user#company.de",
"email": [
"user#company.de"
],
desired file:
{
"id": "aaaa",
"desc": "Service aaa",
"boss":"user#company.de",
"email": [
"user#company.de"
"another_user#company.de"
]
I have this ansible lineinfile module playbook, but I struggle with decent regex. Everything I try just adds new line in the very end of file.
---
- hosts: localhost
gather_facts: no
tasks:
- name: insert line
lineinfile:
path: /home/file.json
state: present
insertafter: " ^ "email": [ "
line: 'another_user#company.de'
How should I write correct regex in this case to write line after the string "email": [ ?

Answer 1

quick comment :
JSON spec mandates an ASCII comma (",") between values of arrays (plus your choice of whitespace(s)), so to make the proposed solutions compliant, they would have to resemble this instead
—— (snippet directly from jq):
{
"id": "aaaa",
"desc": "Service aaa",
"boss": "user#company.de",
"email": [
"user#company.de",
"newline"
]
}

Answer 2

Let's say current file is aa.txt as follows
{
"id": "aaaa",
"desc": "Service aaa",
"boss":"user#company.de",
"email": [
"user#company.de"
],
Use sed command
sed '/"email.*\[/!{p;d;};n;a new line' aa.txt
Output
{
"id": "aaaa",
"desc": "Service aaa",
"boss":"user#company.de",
"email": [
"user#company.de"
new line
],
Alternatively use AWK
awk '1;/"email.*\[/{c=2}c&&!--c{print "new text"}' aa.txt
Output
{
"id": "aaaa",
"desc": "Service aaa",
"boss":"user#company.de",
"email": [
"user#company.de"
new line
],