feat(helm): add support for mongodb operator (#41733)

## Description
> [!TIP]  
> _Add a TL;DR when the description is longer than 500 words or
extremely technical (helps the content, marketing, and DevRel team)._
>
> _Please also include relevant motivation and context. List any
dependencies that are required for this change. Add links to Notion,
Figma or any other documents that might be relevant to the PR._

Adds preview support for the MongoDB operator to replace the old Bitnami
chart. I've been unable to find a seamless alternative to the old chart
and having to maintain our own templates is untenable. This is the
direction that MongoDB is going, so it seems simpler to embrace it.

The Bitnami chart and MongoDB operator options are not mutually
exclusive here to allow for transitioning between the two. However, in
practice the time where both are enabled should be minimal to avoid
confusion and extra resources.

Pros for this approach:
- official MongoDB support, will be better in the long run
- supports single node deployments and replicasets easily with little
effort
- handles upgrades and downgrades (neither of which were supported by
the old chart)
- leapfrog over MongoDB 7 in the Helm chart (?)

Cons:
- operator adds extra overhead in the case of a single node deployment
of MongoDB, have to deal with CRDs, and all that goes with running an
operator
- the transition is going to be awkward. once we are ready to cut out
the old chart, we'll have to figure out a way to ensure users of the old
chart migrate
- no built-in backup support in community operator, but that's not
unique from the old chart
- needs a hook to generate a password, which adds RBAC and job overhead

Once we've gotten through some testing, intent is to share docs on how
to use this for both new installs and how to transition. Then at some
point in the future, create a new major release that forces the
administrator to either migrate or bring in their own MongoDB from an
external source.

Fixes #`Issue Number`  
_or_  
Fixes `Issue URL`
> [!WARNING]  
> _If no issue exists, please create an issue first, and check with the
maintainers if the issue is valid._

https://linear.app/appsmith/issue/APP-14807/task-switch-mongodb-image-from-bitnami-to-mongodb-provided-image

## Automation

/ok-to-test tags=""

### :mag: Cypress test results
<!-- This is an auto-generated comment: Cypress test results  -->
> [!WARNING]
> Tests have not run on the HEAD
92c0eed3526f1064a0a2a632668f7f64357e706a yet
> <hr>Wed, 29 Apr 2026 20:05:39 UTC
<!-- end of auto-generated comment: Cypress test results  -->


## Communication
Should the DevRel and Marketing teams inform users about this change?
- [ ] Yes
- [x] No


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Optional MongoDB Operator deployment path, chart version bump,
operator-managed MongoDB mode, transition support, init/init-container
and DB connection handling, and automatic password-init Job.

* **Documentation**
* New operator/community install guide, README updates, quickstart,
verification, migration and troubleshooting steps.

* **Tests**
* Expanded Helm tests for operator rendering, transition behavior,
password-init hook, and validation errors.

* **Chores**
* Ignore rule for local MongoDB artifacts updated; added values and JSON
schema for operator/community.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

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Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Co-authored-by: subratadeypappu <subrata@appsmith.com>