Add feed fetch frequency form elements

[landonreed]

Checklist

• Appropriate branch selected (all PRs must first be merged to dev before they can be merged to master)
• Any modified or new methods or classes have helpful JSDoc and code is thoroughly commented
• The description lists all applicable issues this PR seeks to resolve
• The description lists any configuration setting(s) that differ from the default settings
• All tests and CI builds passing

Description

Adds form elements to handle setting feed fetch frequency. re ibi-group/datatools-server#346

[evansiroky]

Some comments about adhering to DRY.

[binh-dam-ibigroup]

Please see the code cleanup items I mentioned and update the snapshots. (I don't feel strongly about moving the temporal strings to i18n.)

[evansiroky]

Could be shortened to:

let {fetchFrequency = 'DAYS', fetchInterval = intervals[0]} = props

[landonreed]

What if they're null though? Is that possibility precluded with flow typing? I chose this approach because (if I'm not mistaken) if a null value is passed it will override the default value.

[evansiroky]

Build is failing, otherwise seems fine

[landonreed]

Thanks for the thorough review! Comments addressed in 30c72de.

[binh-dam-ibigroup]

Conditional approval on making tests pass.

[binh-dam-ibigroup]

Using two dropdowns is probably fine for now, although a single dropdown will all options would ultimately work better.

I can imagine a user trying to adjust the frequency from say 1 day to 12 hours. Intuitively they would try to select the interval first, then adjust the frequency unit. Upon selecting 'hours' their number selection would be reset.