Upgrade `openapi-typescript` dependency

[wilsonianb]

To include:

• https://github.com/drwpow/openapi-typescript/pull/968

~Currently not released yet:~ Released in v6.0.0+ https://www.npmjs.com/package/openapi-typescript

[wilsonianb]

Hopefully this isn't still an issue:

• https://github.com/interledger/rafiki/pull/669#discussion_r995716719

[wilsonianb]

I've started a branch for this:

• https://github.com/wilsonianb/rafiki/pull/162

but I appear to be running into:

• https://github.com/drwpow/openapi-typescript/issues/993#issuecomment-1321148446

[wilsonianb]

• https://github.com/interledger/rafiki/pull/996

[wilsonianb]

• [x] upgrade
• [ ] take advantage of the OpenAPI 3.1 benefits of https://github.com/drwpow/openapi-typescript/pull/968
• [ ] determine if we still need to work around https://github.com/drwpow/openapi-typescript/issues/993

[mkurapov]

• Just tried, https://github.com/drwpow/openapi-typescript/issues/993 seems to be an issue still (as of v6.2.0)