Add Seek method based on timestamp about datadistributionmanager

[mariomastrodicasa]

@marcocappolimases as stated in #21 (comment), you are proposing a method which can accept negative values. The same approach can be applied to the Seek method proposed in this issue. One drawback with the actual implementation of Seek with negative values is that backends (librdkafka, OpenDDS) uses negative values for their internal purposes and specific negative values have well-known behavior. Since real offsets are positive monotonic incremental values and negative values are only special, I propose to change the signature of the Seek to add an optional parameter which defines if the offset is Absolute or Relative, so it is possible to distinguish when a negative value refers to something in the past of the data stream or it is a special value. The same behavior can be applied to the Seek method that accepts a timestamp.
In the issue you proposed a DateTme type which is undoubtedly related to .NET (C#). Both C# and Java implementations are wrappers around the C++ implementation: in #21 (comment) there is a proposal about timestamp, but the low layer measures the timestamp as milliseconds from epoch (UTC) and the base type is something similar to the offset one. At C++ level the problem will be to distinguish between Seek method for offset and timestamp: my idea to solve this inchoerence is to add another optional parameter which defines which kind of input is receiving the Seek method. The final signature will be something like the following one:

typedef enum class DDM_SEEKCONTEXT
{
	OFFSET = 0x1,	   /**< Seek on offset */
	TIMESTAMP = 0x2,   /**< Seek on timestamp */
} DDM_SEEKCONTEXT;

typedef enum class DDM_SEEKKIND
{
	ABSOLUTE = 0x1,	   /**< Absolute seek */
	RELATIVE = 0x2,   /**< Relative seek */
} DDM_SEEKKIND;

virtual OPERATION_RESULT SeekChannel(CHANNEL_HANDLE_PARAMETER, int64_t position, DDM_SEEKCONTEXT context = DDM_SEEKCONTEXT::OFFSET, DDM_SEEKKIND kind = DDM_SEEKKIND::ABSOLUTE) = 0;

The previous implementation will be open for further extensions, adding more values to DDM_SEEKCONTEXT and DDM_SEEKKIND, without changing again the low level interface.

[marcocappolimases]

@mariomastrodicasa the solution seems optimal for C++.
I think that the implementation I proposed in the Issue can be used to call transparently both an absolute or a relative seek.