feat: Support string variable in the first argument of @Extension

[chappelo]

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Closing issues

closes #1520

Adds support of string identifiers to be passed into @Extension's attribute key.

This is accomplished by adding ts.isIdentifier checks into getExtensions. If it is an identifier -> getInitializerValue()

If this is a new feature submission:

• Has the issue had a maintainer respond to the issue and clarify that the feature is something that aligns with the goals and philosophy of the project?

Potential Problems With The Approach

Test plan
I added test case to the existing extensions tests.

[chappelo]

Hello, @WoH , if you have time can you take a look at this CI build error please?
https://github.com/lukeautry/tsoa/actions/runs/10871608128/job/30165646700?pr=1677

Looks like lru-cache had some updates last week which might be causing this? are some package updates appropriate?

isaacs/node-lru-cache@5ed947d

[WoH]

Should be fixed now, can you rebase?

[chappelo]

Should be fixed now, can you rebase?

Cool, all works well now. Thanks.
Will mark as ready.