fix(rds/docdb)!: ParameterGroups remove ApplyMethod isUpToDate check

[wotolom]

Description of your changes

RDS: DBParameterGroup, DBClusterParametergroup and DocDB DBClusterParametergroup

• Breaking: switch to custom struct CustomParameters with only fields applyMethod, parameterName and parameterValue (terraform does it the same way)
• Breaking: make parameter fields required in CRD (for RDS these 3 fields where already required by the controller before; for RDS and DocDB those fields were also already required indirectly by AWS )
• reduce Parameter isUpToDate check to only consider parameterValue

Fixes #1708

Breaking changes ToDos/notes for users:

for resources RDS: DBParameterGroup, DBClusterParametergroup and DocDB DBClusterParametergroup claims need to be checked:

• each entry in parameters no longer uses the previously read-only fields allowedValues, applyType, dataType, description, isModifiable, minimumEngineVersion, source and supportedEngineModes
• each entry in parameters requires the only use of all 3 the fields applyMethod, parameterName and parameterValue

I have:

• Read and followed Crossplane's [contribution process].
• Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

Manually

[MisterMX]

LGTM. Thanks @wotolom.

@haarchri can you take a second look at these changes?

[wotolom]

Ready for review now as I got the confirmation from AWS support, that this is indeed the expected behavior for the field ApplyMethod.

[wotolom]

@haarchri Considering the breaking changes, I added a potential ToDo note, that can be added to the release notes for users.

[haarchri]

Sounds good to me - thanks