Support multiple instruments in addFromConfig

[jtniehof]

The addFromConfig config file format only supports a single instrument. The docs say:

# [instrument] <- once and only once with
#   instrument_name  (string)

Including multiple "instrument_name" lines gives an "option already exists" error, which makes sense. But the database structure does support multiple instruments per satellite.

Relation to an issue

Discussion in #78.

Proposed enhancement

Desired behavior needs to be fleshed out further. In particular:

• How is this represented in the config file.
• How are products mapped to instruments (since this is not currently in the format).

Alternatives

To be fleshed out further.

OS, Python version, and dependency version information:

Linux-4.15.0-143-generic-x86_64-with-Ubuntu-18.04-bionic
sys.version_info(major=2, minor=7, micro=17, releaselevel='final', serial=0)
sqlalchemy=1.1.11

Version of dbprocessing

Branch from #78

Closure condition

This issue should be closed when behavior is fully defined, implemented, tested, and merged.