Support configuration of system-wide default locale

[Gepardgame]

Description

Helps #992 to add system wide default language.
Simple adds a ConfigProperty where the value can be stored, which is also publicly available

Addressed Issue

Fixes #991

Additional Details

Checklist

• I have read and understand the contributing guidelines
  - [ ] This PR fixes a defect, and I have provided tests to verify that the fix is effective
• This PR implements an enhancement, and I have provided tests to verify that it works as intended
  - [ ] This PR introduces changes to the database model, and I have added corresponding update logic
  - [ ] This PR introduces new or alters existing behavior, and I have updated the documentation accordingly

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.01% (target: -1.00%)	✅ 100.00% (target: 70.00%)

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (b8d4866)	21934	17253	78.66%
Head commit (8d13510)	21947 (+13)	17266 (+13)	78.67% (+0.01%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#4136)	2	2	100.00%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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