[core split] Service: mongodb

[Xuanwo]

This issue tracks splitting the service mongodb out of core as part of the core-split effort.

Tracking issue: #6829

Please follow the steps in the tracking issue strictly:

• keep public API/behavior unchanged;
• move code into the new crate layout described there;
• add/update feature flags and tests as required;
• open a PR and link it to #6829.

[Aman202600]

@Xuanwo Please assign me this issue.

[Xuanwo]

@Xuanwo Please assign me this issue.

Assigned, have fun!

[Aman202600]

@Xuanwo Thanks for assigning it to me! I’ll begin working on this. Will reach out if I need any help. 😊