API v1 allow multiple slashes in the path before "api"

[vbaranov]

Resolves #9194

Motivation

//api/v1 path is prohibited.

Changelog

Allow multiple slashes in the path before "api" for api v1 requests in order to make requests like this workable:

curl -s "http://localhost:4000//api/v1?module=contract&action=listcontracts&offset=1"

Checklist for your Pull Request (PR)

• I added an entry to CHANGELOG.md with this PR
• If I added new functionality, I added tests covering it.
• If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.
• I checked whether I should update the docs and did so by submitting a PR to https://github.com/blockscout/docs
• If I added/changed/removed ENV var, I submitted a PR to https://github.com/blockscout/docs to update the list of env vars at https://github.com/blockscout/docs/blob/master/for-developers/information-and-settings/env-variables.md and I updated the version to master in the Version column. Changes will be reflected in this table: https://docs.blockscout.com/for-developers/information-and-settings/env-variables.
• If I add new indices into DB, I checked, that they are not redundant with PGHero or other tools