added a clang-format file for formatting c++ src code

.clang-format

+# SPDX-FileCopyrightText: 2023 Max Planck Institute for Meteorology
+# SPDX-License-Identifier: BSD-3-Clause
+
+BasedOnStyle: LLVM
+
+AlwaysBreakTemplateDeclarations: true
+AlignAfterOpenBracket: Align
+AlignConsecutiveAssignments: Consecutive
+AlignConsecutiveBitFields: Consecutive
+AlignEscapedNewlines: Right
+AlignOperands: AlignAfterOperator
+AlignTrailingComments: true
+AllowAllArgumentsOnNextLine: true
+AllowAllParametersOfDeclarationOnNextLine: true
+AllowShortFunctionsOnASingleLine: true
+AllowShortLambdasOnASingleLine: All
+AttributeMacros: [
+                  '_ALIGNAS_TYPE',
+                  '_ALIGNAS',
+                  '_LIBCPP_ALIGNOF',
+                  '_LIBCPP_ALWAYS_INLINE',
+                  '_LIBCPP_CONSTEXPR_SINCE_CXX14',
+                  '_LIBCPP_CONSTEXPR_SINCE_CXX17',
+                  '_LIBCPP_CONSTEXPR_SINCE_CXX20',
+                  '_LIBCPP_CONSTEXPR_SINCE_CXX23',
+                  '_LIBCPP_CONSTEXPR',
+                  '_LIBCPP_CONSTINIT',
+                  '_LIBCPP_DEPRECATED_IN_CXX11',
+                  '_LIBCPP_DEPRECATED_IN_CXX14',
+                  '_LIBCPP_DEPRECATED_IN_CXX17',
+                  '_LIBCPP_DEPRECATED_IN_CXX20',
+                  '_LIBCPP_DEPRECATED_IN_CXX23',
+                  '_LIBCPP_DEPRECATED',
+                  '_LIBCPP_DISABLE_EXTENSION_WARNING',
+                  '_LIBCPP_EXCLUDE_FROM_EXPLICIT_INSTANTIATION',
+                  '_LIBCPP_EXPORTED_FROM_ABI',
+                  '_LIBCPP_EXTERN_TEMPLATE_TYPE_VIS',
+                  '_LIBCPP_FALLTHROUGH',
+                  '_LIBCPP_HIDDEN',
+                  '_LIBCPP_HIDE_FROM_ABI_AFTER_V1',
+                  '_LIBCPP_HIDE_FROM_ABI',
+                  '_LIBCPP_METHOD_TEMPLATE_IMPLICIT_INSTANTIATION_VIS',
+                  '_LIBCPP_NO_SANITIZE',
+                  '_LIBCPP_NO_UNIQUE_ADDRESS',
+                  '_LIBCPP_NOALIAS',
+                  '_LIBCPP_OVERRIDABLE_FUNC_VIS',
+                  '_LIBCPP_STANDALONE_DEBUG',
+                  '_LIBCPP_TEMPLATE_DATA_VIS',
+                  '_LIBCPP_TEMPLATE_VIS',
+                  '_LIBCPP_THREAD_SAFETY_ANNOTATION',
+                  '_LIBCPP_USING_IF_EXISTS',
+                  '_LIBCPP_WEAK',
+                 ]
+
+
+BinPackArguments: false
+BinPackParameters: false
+BreakBeforeConceptDeclarations: true
+BreakInheritanceList: BeforeColon
+BraceWrapping:
+  AfterCaseLabel: false
+  AfterClass: false
+  AfterControlStatement: false
+  AfterEnum: false
+  AfterFunction: true
+  AfterNamespace: true
+  AfterObjCDeclaration: false
+  AfterStruct: false
+  AfterUnion: false
+  BeforeCatch: false
+  BeforeElse: false
+  IndentBraces: false
+
+# libc++ has some long names so we need more than the 80 column limit imposed by LLVM style, for sensible formatting
+ColumnLimit:    100
+
+EmptyLineAfterAccessModifier: Never
+EmptyLineBeforeAccessModifier: Always
+
+# libc++'s preferred indentions of preprocessor statements.
+IndentPPDirectives: AfterHash
+IndentWidth:     4
+IndentWrappedFunctionNames: false
+IndentRequires: true
+InsertTrailingCommas: Wrapped
+
+KeepEmptyLinesAtTheStartOfBlocks: false
+
+NamespaceIndentation: All
+
+MaxEmptyLinesToKeep: 1
+
+PackConstructorInitializers: NextLine
+PointerAlignment: Left
+PenaltyIndentedWhitespace: 2
+PenaltyBreakBeforeFirstCallParameter: 30
+PenaltyBreakComment: 10
+PenaltyBreakFirstLessLess: 0
+PenaltyBreakString: 10
+PenaltyExcessCharacter: 100
+PenaltyReturnTypeOnItsOwnLine: 60
+
+Standard: c++20
+SpacesInAngles: Leave
+SortIncludes: true
+
+TabWidth: 4
+
+UseTab: Never
+UseCRLF: false
\ No newline at end of file