Add examples for CurrentClamp* types to icephys tutorial

[ehennestad]

Motivation

Reach 100% tutorial coverage for NWB Types. Mirroring https://github.com/NeurodataWithoutBorders/pynwb/pull/2004

How to test the behavior?

Run icephys tutorial

Checklist

• [x] Have you ensured the PR description clearly describes the problem and solutions?
• [x] Have you checked to ensure that there aren't other open or previously closed Pull Requests for the same change?
• [x] If this PR fixes an issue, is the first line of the PR description fix #XX where XX is the issue number?

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.16%. Comparing base (e070e20) to head (c0405c0).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #632 +/- ## ======================================= Coverage 95.16% 95.16% ======================================= Files 113 113 Lines 4734 4734 ======================================= Hits 4505 4505 Misses 229 229 ```

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