[Search] Remove references to keyfile secret in snippets and tests

[fealebenpae]

Summary

With the changes in #527 mongot no longer requires access to the replica set's keyfile. This cleans up tests and doc snippets that are still referencing it.

Proof of Work

Checklist

• Have you linked a jira ticket and/or is the ticket in the title?
• Have you checked whether your jira ticket required DOCSP changes?
• Have you added changelog file?
  • use skip-changelog label if not needed
  • refer to Changelog files and Release Notes section in CONTRIBUTING.md for more details

[github-actions]

⚠️ (this preview might not be accurate if the PR is not rebased on current master branch)

MCK 1.6.0 Release Notes

New Features

• MongoDBCommunity: Added support to configure custom cluster domain via newly introduced spec.clusterDomain resource field. If spec.clusterDomain is not set, environment variable CLUSTER_DOMAIN is used as cluster domain. If the environment variable CLUSTER_DOMAIN is also not set, operator falls back to cluster.local as default cluster domain.
• Helm Chart: Introduced two new helm fields operator.podSecurityContext and operator.securityContext that can be used to configure securityContext for Operator deployment through Helm Chart.
• MongoDBSearch: Switch to gRPC and mTLS for internal communication
  Since MCK 1.4 the mongod and mongot processess communicated using the MongoDB Wire Protocol and used keyfile authentication. This release switches that to gRPC with mTLS authentication. gRPC will allow for load-balancing search queries against multiple mongot processes in the future, and mTLS decouples the internal cluster authentication mode and credentials among mongod processes from the connection to the mongot process. The Operator will automatically enable gRPC for existing and new workloads, and will enable mTLS authentication if both Database Server and MongoDBSearch resource are configured for TLS.
• MongoDBSearch: MongoDB deployments using X509 internal cluster authentication are now supported. Previously MongoDB Search required SCRAM authentication among members of a MongoDB replica set. Note: SCRAM client authentication is still required, this change merely relaxes the requirements on internal cluster authentication.
• MongoDBSearch: Updated the default mongodb/mongodb-search image version to 0.55.0. This is the version MCK uses if .spec.version is not specified.

Bug Fixes

• Fixed parsing of the customEnvVars Helm value when values contain = characters.
• ReplicaSet: Blocked disabling TLS and changing member count simultaneously. These operations must now be applied separately to prevent configuration inconsistencies.
• MongoDBSearch now records the reconciled mongot version in status and exposes it via a dedicated kubectl print column.
• Fixed inability to specify cluster-wide privileges in custom roles.

Other Changes

• Simplified MongoDB Search setup: Removed the custom Search Coordinator polyfill (a piece of compatibility code previously needed to add the required permissions), as MongoDB 8.2.0 and later now include the necessary permissions via the built-in searchCoordinator role.
• kubectl-mongodb plugin: cosign, the signing tool that is used to sign kubectl-mongodb plugin binaries, has been updated to version 3.0.2. With this change, released binaries will be bundled with .bundle files containing both signature and certificate information. For more information on how to verify signatures using new cosign version please refer to -> https://github.com/sigstore/cosign/blob/v3.0.2/doc/cosign_verify-blob.md