fix init-mongo.sh

[m4r1k]

The updated init-mongo.sh is broken.

the variable MONGO_AUTHSOURCE lacks the $ sign making it a usable variable
the verb use in MongoDB does not support double quoting the DB name

As per #108 (comment) applying the fix to readme-vars.yaml template. @thespad let me know if anything else is missing.

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• I have read the contributing guideline and understand that I have made the correct modifications

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Description:

Benefits of this PR and context:

How Has This Been Tested?

Pull latest MongoDB 7.0.12, and run it with the init script provided in this repo on main branch.
The unifi-db logs will gives some details on the error, executing once more the init script will reveal all that is wrong.

root@9dabf25a221d:/docker-entrypoint-initdb.d# bash init-mongo.sh
Current Mongosh Log ID:	66b9e3ef84b242a13b149f47
Connecting to:		mongodb://127.0.0.1:27017/?directConnection=true&serverSelectionTimeoutMS=2000&appName=mongosh+2.2.10
Using MongoDB:		7.0.12
Using Mongosh:		2.2.10

For mongosh info see: https://docs.mongodb.com/mongodb-shell/

test> use "{MONGO_AUTHSOURCE}"
MongoshInvalidInputError: [COMMON-10001] Invalid database name: "{MONGO_AUTHSOURCE}"
test> db.auth("root", "[SNIP]")
MongoServerError[AuthenticationFailed]: Authentication failed.
test> use "unifi"
MongoshInvalidInputError: [COMMON-10001] Invalid database name: "unifi"
test> db.createUser({
...   user: "unifi",
...   pwd: "[SNIP]",
...   roles: [
...     { db: "unifi", role: "dbOwner" },
...     { db: "unifi_stat", role: "dbOwner" }
...   ]
... })
MongoServerError[Unauthorized]: Command createUser requires authentication

Source / References:

[LinuxServer-CI]

I am a bot, here is the pushed image/manifest for this PR:

ghcr.io/linuxserver/lspipepr-unifi-network-application:8.3.32-pkg-1e1f6820-dev-e99b2d4e345509553e4124c8b8c56b25b63a37cd-pr-109