[1786] Implement textual export of RequirementConstraintMembership

[adaussy]

Bug: #1786

PLEASE READ ALL ITEMS AND CHECK ONLY RELEVANT CHECKBOXES BELOW

Auto review

• Have you reviewed this PR? Please do a first quick review, It is very useful to detect typos and missing copyrights, check comments, check your code... The reviewer will thank you for that :)

Project management

• Has the pull request been added to the relevant milestone?
• Have the priority: and pr: labels been added to the pull request? (In case of doubt, start with the labels priority: low and pr: to review later)
• Have the relevant issues been added to the pull request?
• Have the relevant labels been added to the issues? (area:, type:)
• Have the relevant issues been added to the same project milestone as the pull request?

Changelog and release notes

• Has the CHANGELOG.adoc + doc/content/modules/user-manual/pages/release-notes/YYYY.MM.0.adoc been updated to reference the relevant issues?
• Have the relevant API breaks been described in the CHANGELOG.adoc?
• Are the new / upgraded dependencies mentioned in the relevant section of the CHANGELOG.adoc?
• In case of a change with a visual impact, are there any screenshots in the doc/content/modules/user-manual/pages/release-notes/YYYY.MM.0.adoc?
• In case of a key change, has the change been added to Key highlights section in doc/content/modules/user-manual/pages/release-notes/YYYY.MM.0.adoc?

Documentation

• Have you included an update of the documentation in your pull request? Please ask yourself if an update (installation manual, user manual, developer manual...) is needed and add one accordingly.

Tests

• Is the code properly tested? Any pull request (fix, enhancement or new feature) should come with a test (or several). It could be unit tests, integration tests or cypress tests depending on the context. Only doc and releng pull request do not need for tests.