[REQ] Replace use of no action values with C++17 std::optional

[drmason789]

and use resistanceRequest.has_value() and resistanceRequest.reset() instead of having a "no action constant". If you are agreeable, I will do this for the resistance, inclination and power requests, in a different PR.

yes sure! thanks!

Originally posted by @cagnulein in #2174 (comment)

[drmason789]

I've volunteered to do this.

For each varname that's optional

• replace comparisons with the "no value" value with varname.has_value()
• replace comparisons with other values with varname.value()
• use varname.value_or(...) where possible
• replace assignment of the "no value" value with varname.reset()

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.