ipfs: add options to disable

- CPPFLAGS: `-DCURL_DISABLE_IPFS`
- configure: `--disable-ipfs`
- cmake: `-DCURL_DISABLE_IPFS=ON`

Fixes #14824
Closes #14827

curl: move IPFS code into src/tool_ipfs.[ch]

- convert ensure_trailing into ensure_trailing_slash
- strdup the URL string to own it proper
- use shorter variable names
- combine

curl: move IPFS code into src/tool_ipfs.[ch]

- convert ensure_trailing into ensure_trailing_slash
- strdup the URL string to own it proper
- use shorter variable names
- combine some expressions
- simplify error handling in ipfs_gateway()
- add MAX_GATEWAY_URL_LEN + proper bailout if maximum is reached
- ipfs-gateway.d polish and simplification
- shorten ipfs error message + make them "synthetic"

Closes #12281

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