feat(mongodb): support rotation_statements for static roles

[pbromb]

Description

This PR enhances the MongoDB database plugin to support rotation_statements for static roles, similar to the MySQL plugin behavior.

• Support rotation_statements during password rotation (UpdateUser), executing a list of JSON statements shaped like:
  • {"db":"admin","command":{...}}
• Template variables supported in each statement: {{username}}, {{password}} (and {{name}})
• Ordered command execution: decode command into an ordered bson.D before calling RunCommand (fixes multi-key command errors)
• Optional ignore_errors per statement to allow idempotent rotations (e.g. ignore “user already exists” for createUser), supporting friendly tokens like UserAlreadyExists / DuplicateKey

Example:

"rotation_statements" = [
  "{\"db\":\"admin\",\"command\":{\"createUser\":\"{{username}}\",\"pwd\":\"{{password}}\",\"roles\":[]},\"ignore_errors\":[\"UserAlreadyExists\"]}",
  "{\"db\":\"admin\",\"command\":{\"updateUser\":\"{{username}}\",\"pwd\":\"{{password}}\",\"roles\":[{\"role\":\"readWrite\",\"db\":\"example\"}]}}"
]

For comparison, in the MySQL plugin this can be achieved by providing rotation_statements, e.g.:

"rotation_statements" = [
    "CREATE USER IF NOT EXISTS '{{name}}'@'%' IDENTIFIED BY '{{password}}';",
    "GRANT ALL ON example.* TO '{{name}}'@'%';",
    "ALTER USER '{{name}}'@'%' IDENTIFIED BY '{{password}}';"
]

This PR brings equivalent rotation_statements support to the MongoDB plugin, which previously did not support rotation statements for static roles.

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