build(mvn): add GitLab repository for perun-openapi dependency

Description

build(mvn): add GitLab repository for perun-openapi dependency

• added GitLab Perun group repository for the perun-openapi dependency
• configured local maven settings for authorization to the repo
• use personal access token in local-settings.xml to access repo locally
• use CI token in ci-settings.xml for work with CI
• upgraded to Spring boot 3.1.4 to allow compiling with Java 21, there should be no major changes

How to test

Set access token in local-settings.xml in order to access the GitLab maven repo and try to mvn install, build should be successful.

Author's checklist

• I have followed the contribution guidelines
• This MR has been tested or does not change functionality
• I have added relevant merge request dependencies (if this MR has any)
• I have added the correct labels
• I have assigned reviewers (if any are relevant)
• I have edited the documentation (if the changes require it) or I have noted the need for the change if I do not have access to the documentation
• I have marked all introduced BREAKING CHANGES or necessary DEPLOYMENT NOTES in the commit message(s)

Reviewer's checklist

• This MR has been tested or does not change functionality
• This MR has correct commit message format

Other information

I encountered some issues with mvn compiler not recognizing my Java version (might be related to Spring boot 3, since I do not encounter this problem in the perun project), finally managed to run it through IDEA upon changing Build, Execution, Deployment > Compiler > Java Compiler > Target bytecode version to 17.

Related issues

re STR-1215