Write output ecsv file with optical throughput info

Description

This merge request writes the output of the throughput calibration in the form of an astropy.Table serialized to ecsv format. Following points to discuss:

• Additional information to store / information to remove
• Which storage strategy to adopt (currently row-wise, but column-wise could be faster according to astropy.Table documentation
• Path of the output file should be common to other outputs coming from the calibpipe (pre-database integration)
• Output file format: ecsv or fits

Related Issue

Closes #48 (closed). The output of the throughput calibration was stored in the proper containers, but not saved to file.

Closes #39 (closed).

How Has This Been Tested?

The throughput calibration test has been properly updated.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.