[NU-983] Add missing validations to base components

[mslabek]

Describe your changes

The goal is to make the validation consistent between FE and BE for base components by adding BE validations that are done only on the FE.

Main goal - Bringing base components FE validations to BE

In base components these validations are:

1. Switch - expression in edges - NotNullParameterValidator
2. Filter - expression - NotNullParameterValidator
3. Variable - expression - MandatoryParameterValidator
4. MapVariable:
   • field key - unique value in relation to other field names in the node
   • field value - MandatoryParameterValidator

Also, this removes the default Mandatory value validation on the FE if no validator was set. This is going to be removed anyways after removing the FE validators.

Api changes

In MapVariable (and FragmentOuptut) and in Switch the validated parameters are not standard fields and they require their own solutions to be correctly displayed. BE can control under which field the error is displayed by the fieldName in the NodeValidationError object.

1. In switch nodes fieldName = name of the node to which the choice points to
2. In nodes using a user-controlled dynamic map of key-value pairs (MapVariable (and FragmentOuptut) the simplest solution was to rely on index of the field. This means that FE now has to display them in order of the index:
   • for keys fieldName = $fields-${index}-$key
   • for values fieldName = $fields-${index}-$value

Problems

1. Drag'n'drop in MapVariable - this is problematic - after doing drag'n'drop the errors are displayed "as previously" until the next validation comes with the index after dropping. Solving this is problematic and imo out of scope of this PR.

Checklist before merge

• Related issue ID is placed at the beginning of PR title in [brackets] (can be GH issue or Nu Jira issue)
• Code is cleaned from temporary changes and commented out lines
• Parts of the code that are not easy to understand are documented in the code
• Changes are covered by automated tests
• Showcase in dev-application.conf added to demonstrate the feature
• Documentation added or updated
• Added entry in Changelog.md describing the change from the perspective of a public distribution user
• Added MigrationGuide.md entry in the appropriate subcategory if introducing a breaking change
• Verify that PR will be squashed during merge

[github-actions]

created: #5129
⚠️ Be careful! Snapshot changes are not necessarily the cause of the error. Check the logs.