Implement an AST to support or conditions in $filter

[Sjustein]

Implement an AST or some kind of lexer to more easily parse complex strings like the filter part of the odata query. To scope this issue a bit, only parse the currently supported grammar, but add support for and and or. Nesting statements should be left to future issues.

Acceptance criteria:

• An AST is used to parse the filter part of the odata query instead of the current regex.
• If it is determined implementing the AST has benefits for orderBy as well, implement it and support the choice in the PR.
• The AST parses the filter string exactly the same way as the current regex, apart from also supporting and and or.
• Tests are written to properly test the AST and the pipeline passes.