Online retail giant Amazon.com will open its first office in Massachusetts next year, and eventually could hire as many as 150 people to staff a Cambridge outpost likely to develop software for the delivery of digital media - books, music, video - and conduct “big idea’’ research and development. The Seattle company declined to comment about its plans, but it is actively recruiting engineering and research talent and seeking office space in Kendall Square, according to two people with knowledge of the search, but who requested anonymity because they are not authorized to speak about these efforts. An Amazon office will “contribute heavily to the ecosystem. We continue to be a talent pool that big companies want to tap into,’’ said Jeffrey Bussgang, a venture capitalist with Flybridge Capital Partners.