[master] MongoDB returner reuse database connections

[ilinas]

What does this PR do?

Improves mongo_future_return performance when used as master job cache by reusing database connections.

Probably no difference for mongo_return, but updated anyway for consistency.

What issues does this PR fix or reference?

Fixes: #55999

Previous Behavior

A new database connection established every time a returner function is called.

New Behavior

A database connection is reused when multiple functions are called in a single run.

Merge requirements satisfied?

• Docs
• Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• Tests written/updated

Commits signed with GPG?

No

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[provanguard]

We have tested this on production already and it works. Looking forward to getting it integrated. Great work @ilinas !

[ilinas]

I cannot help but notice that the files have been removed from the source code. Are they being moved to another repository or simply gone? What should I do with this PR? Please advise.

[network-shark]

@ilinas It seems that mongo stuff will be moved to extensions , but there is no mongo returner in this repo https://github.com/salt-extensions/saltext-mongodb/tree/main/src/saltext/mongodb , but think this will be the right place .