Allow str type in Feed

[BrianJKoopman]

Description

The switch to using the G3Timesample object to store data instead of IrregBlockDouble in #128 allows us to store strings in a G3String. The OCS Feeds check the type of data being passed to them and previously strings were restricted. This allows them to be published on Feeds.

Motivation and Context

The M1000 Agent being developed in socs will pass string descriptions of the state of the hardware along with integers which encode those strings. Without this patch the strings cause an error to be raised when publishing to the Feed.

How Has This Been Tested?

Tests updated to try passing a string to the feed (and pass locally.) I've also been developing the M1000 Agent and passing strings from it based on a patched OCS with this change.

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 not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• Unless I am preparing a release, I have opened this PR onto the develop branch.

[mhasself]

Great, let's get this in... need it for ACU, too.