Add DC bias and measurement time params to Keysight E4980A driver

[Akshita07]

Changes proposed in this pull request:

• Adds DC Bias parameters
• Adds measurement time parameter
• Adds method to check installed option number

To Do:

• Check and add valid voltage range
• Update meas time parameter (implementation in progress)
• Test updates on actual instrument

@astafan8

[codecov]

Codecov Report

Merging #2502 (73cdef5) into master (76a0f9a) will decrease coverage by 0.04%.
The diff coverage is 18.51%.

@@            Coverage Diff             @@
##           master    #2502      +/-   ##
==========================================
- Coverage   62.34%   62.30%   -0.05%     
==========================================
  Files         200      200              
  Lines       26379    26404      +25     
==========================================
+ Hits        16447    16450       +3     
- Misses       9932     9954      +22     

[astafan8]

Looks great!

Just one small question/note, hopefully without the need for any adjustments