Update preciceDict to comply with upcoming schema changes

[vidulejs]

The new preCICE schema will have additional options for fields, to specify solver_name and operation. This means that readData and writeData in preciceDict would be dictionaries instead of lists, so that these additional options can be parsed. For example:

  Interface1
  {
    mesh              Fluid-Mesh;
    patches           (interface);
    
    readData
    {
      Heat-Flux
      {
      	solver_name	T;
      	operation	gradient;
      };
    };
    
    writeData
    {
      Temperature
      {
      	solver_name	T;
      	operation	value;
      };	
    };
  };

I tried to look into ways to keep backwards compatibility with the lists, but this may not be desirable. The new schema warrants breaking changes. In order to read old config files, we'd have to check if it's a list or a dict. OpenFOAM does not make this easy... I tried to use the ITstream (Input Token Stream) to check whether the token is ( for list or { for dict. However the ITstream & dictionary.lookup(word &keyword) works only if i'm looking up a list and not a dict. I would need to write a custom parser. Similar issue on cfd-online forums.

TODO list:

• I updated the documentation in docs/
• I added a changelog entry in changelog-entries/ (create directory if missing)

[MakisH]

For the review, I think we would need also a corresponding draft PR in the tutorials, porting at least one case (e.g., the flow-over-heated-plate).

[MakisH]

Based on the latest state (list of dictionaries), it looks like we need a different, solution as described in precice/preeco-orga#38 (comment)

[MakisH]

As operation, we could distinguish between gradient and normal-gradient (writing to be checked for consistency), to account for #380

[MakisH]

To release it with v1.4.0, we need to implement it in a backwards-compatible way.