oidcccl: HTTP client should respect timeouts

[pritesh-lahoti]

Currently, the HTTP client used by the code in the OIDC feature does not respect any timeouts we might have set on our default HTTP client. The go-oidc and oauth2 packages require a custom HTTP client to be set within the context. This change sets an HTTP client with the default timeout (as in pkg/util/httputil) within the context.

Epic: CRDB-38416

Release note: None

[cockroach-teamcity]

This change is 

[dhartunian]

@pritesh-lahoti SGTM

[pritesh-lahoti]

TYFTRs! bors r=dhartunian,souravcrl

[craig[bot]]

Build succeeded:

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