[A11y] - Label does not convey purpose of control

### Current Behaviour
`The label does not convey the purpose of the control.
`

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### Expected Behaviour
`RULE : Labels MUST be meaningful. HOW TO FIX: Fix this issue by providing a descriptive label for the control. `

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### Impact

- [ ] Blocker
- [x] Serious
- [ ] Critical
- [ ] Moderate
- [ ] Minor

### Issue Details

View Issue 1686753

_**Auditor ID**_ : [1686753](https://axeauditor.dequecloud.com/issue-global-search?searchKeyword=1686753&searchOn=id)

_**description**_ : Show/ Hide Panel
Element location: In the "Default, With Optional Group Headings" sections.

Expected name:
Show Items panel/ Hide items panel
Show Grouped Items panel/ Hide Grouped Items panel

_**Page Name**_ : Two column panel

_**source**_ : ``

_**Screenshots**_ : [Show panel](https://axeauditor.dequecloud.com/api/v1/file/07591cce-dbbb-11ee-970b-2fbb3061cdf5)

View Issue 1686754

_**Auditor ID**_ : [1686754](https://axeauditor.dequecloud.com/issue-global-search?searchKeyword=1686754&searchOn=id)

_**description**_ : Grouped items region label is given as "OPTIONAL GROUP HEADING" instead of "Grouped Items".

Element location: In the section "With Optional Group Headings".

_**Page Name**_ : Two column panel

_**source**_ : `

...
`

_**Screenshots**_ : [Group label](https://axeauditor.dequecloud.com/api/v1/file/99e4f298-dbbb-11ee-b8a4-5b510f78179a)

Start with the Two column panel examples described in the issue and search for the control and group-heading markup shown in the source snippets. Verify the show/hide controls use the requested descriptive names and that the grouped-items region is labeled "Grouped Items"; confirm the rendered examples no longer report the auditor findings.

Written by the indexing model from the issue text.