Update description for property changedAt in week based capacity group

[nhaenis]

Description

Changed description for property changedAt in model
io.catenax.week_based_capacity_group

Closes #156

MS2 Criteria

(to be filled out by PR reviewer)

• the model validates with the BAMM SDS SDK in the version specified in the Readme.md of this repository by the time of the MS2 check (e.g., 'java -jar bamm-cli.jar -i <path-to-aspect-model> -v ). The BAMM CLI is available here and in GitHub
• use Camel-Case (e.g., "MyModelElement" or "TimeDifferenceGmtId", when in doubt follow https://google.github.io/styleguide/javaguide.html#s5.3-camel-case)
• the identifiers for all model elements start with a capital letter except for properties
• the identifier for properties starts with a small letter
• all model elements at least contain the fields "name" and "description" in English language.
• no duplicate names or preferredNames within an Aspect (e.g. a Property and the referenced Characteristic should not have the same name)
• the versioning in the URN follows semantic versioning, where minor version bumps are backwards compatible and major version bumps are not backwards compatible.
• use abbreviations only when necessary and if these are sufficiently common
• avoid redundant prefixes in property names (consider adding properties to an enclosing Entity or even adapt the namespace of the model elements, e.g., instead of having two properties DismantlerId and DismantlerName use an Entity Dismantler with the properties name and id or use a URN like io.catenax.dismantler:0.0.1)
• fields preferredName and description are not the same
• preferredName should be human readable and follow normal orthography (e.g., no camel case but normal word separation)
• name of aspect is singular except if it only has one property which is a Collection, List or Set. In theses cases, the aspect name is plural.
• units are referenced from the BAMM unit catalog whenever possible
• use constraints to make known constraints from the use case explicit in the aspect model
• when relying on external standards, they are referenced through a "see" element
• all properties with an simple type have an example value
• metadata.json exists with status "release"
• file RELEASE_NOTES.md exists and contains entries for proposed model changes
• all contributors to this model are mentioned in copyright header of model file

MS3 Criteria

(to be filled out by semantic modeling team before merge to main-branch)

• All required reviewers have approved this PR (see reviewers section)
• The new aspect (version) will be implemented by at least one data provider
• The new aspect (version) will be consumed by at least one data consumer
• There exists valid test data
• In case of a new (incompatible) major version to an existing version, a migration strategy has been developed
• The model has at least version '1.0.0'