cohttp & uri: add x-maintenance-intent from upstream

[hannesm]

see mirage/ocaml-cohttp#1107 mirage/ocaml-uri#180 //cc @samoht

[mseri]

I have left a question on cohttp, I'd wait for the answer before merging this

[raphael-proust]

ping @samoht re: mirage/ocaml-cohttp#1107 (comment)

[hannesm]

/cc @samoht -- would be great if you could approve or disapprove

[hannesm]

Paging @samoht for his opinion about this.

[samoht]

I've checked with @rgrinberg and it's ok to drop support for old versions of cohttp

[hannesm]

Thanks @samoht. From a git grep in the public opam-repository, it looks like {>= "2.5.7" & < "3.0.0" | >= "5.1.1" & < "6.0.0"}

Details

opam-repository$ git grep '"cohttp' | grep '.v0'
packages/async_rpc_websocket/async_rpc_websocket.v0.15.0/opam:  "cohttp_async_websocket" {>= "v0.15" & < "v0.16"}
packages/async_rpc_websocket/async_rpc_websocket.v0.15.0/opam:  "cohttp-async"           {>= "2.5.6" & < "3.0.0" | >= "5.0.0"}
packages/async_rpc_websocket/async_rpc_websocket.v0.16.0/opam:  "cohttp_async_websocket" {>= "v0.16" & < "v0.17"}
packages/async_rpc_websocket/async_rpc_websocket.v0.16.0/opam:  "cohttp-async"           {>= "2.5.7" & < "3.0.0" | >= "5.1.1" & < "6.0.0"}
packages/async_rpc_websocket/async_rpc_websocket.v0.17.0/opam:  "cohttp_async_websocket" {>= "v0.17" & < "v0.18"}
packages/async_rpc_websocket/async_rpc_websocket.v0.17.0/opam:  "cohttp-async"           {>= "2.5.7" & < "3.0.0" | >= "5.1.1" & < "6.0.0"}
packages/bonsai/bonsai.v0.15.0/opam:  "cohttp-async"             {>= "2.5.6" & < "3.0.0" | >= "5.0.0"}
packages/bonsai/bonsai.v0.15.1/opam:  "cohttp-async"             {>= "2.5.6" & < "3.0.0" | >= "5.0.0"}
packages/bonsai/bonsai.v0.16.0/opam:  "cohttp-async"             {>= "2.5.7" & < "3.0.0" | >= "5.1.1" & < "6.0.0"}
packages/bonsai/bonsai.v0.17.0/opam:  "cohttp-async"                {>= "2.5.7" & < "3.0.0" | >= "5.1.1" & < "6.0.0"}
packages/cohttp_async_websocket/cohttp_async_websocket.v0.15.0/opam:  "cohttp" {>= "2.5.6" & < "6.0.0~"}
packages/cohttp_async_websocket/cohttp_async_websocket.v0.15.0/opam:  "cohttp-async" {>= "2.5.6" & < "3.0.0" | >= "5.0.0" & < "6.0.0~"}
packages/cohttp_async_websocket/cohttp_async_websocket.v0.16.0/opam:  "cohttp"          {>= "2.5.6"}
packages/cohttp_async_websocket/cohttp_async_websocket.v0.16.0/opam:  "cohttp-async"    {>= "2.5.7" & < "3.0.0" | >= "5.1.1" & < "6.0.0~"}
packages/cohttp_async_websocket/cohttp_async_websocket.v0.17.0/opam:  "cohttp"          {>= "2.5.6"}
packages/cohttp_async_websocket/cohttp_async_websocket.v0.17.0/opam:  "cohttp-async"    {>= "2.5.7" & < "3.0.0" | >= "5.1.1" & < "6.0.0"}
packages/cohttp_static_handler/cohttp_static_handler.v0.15.0/opam:  "cohttp-async" {>= "2.5.6" & < "3.0.0" | >= "5.0.0"}
packages/cohttp_static_handler/cohttp_static_handler.v0.16.0/opam:  "cohttp-async" {>= "2.5.7" & < "3.0.0" | >= "5.1.1" & < "6.0.0"}
packages/cohttp_static_handler/cohttp_static_handler.v0.17.0/opam:  "cohttp-async" {>= "2.5.7" & < "3.0.0" | >= "5.1.1" & < "6.0.0"}
packages/sentry/sentry.v0.10.1/opam:  "cohttp" {>= "2.0.0"}
packages/sentry/sentry.v0.10.1/opam:  "cohttp-async" {>= "2.0.0"}
packages/sentry/sentry.v0.11.0/opam:  "cohttp" {>= "2.0.0"}
packages/sentry/sentry.v0.11.0/opam:  "cohttp-async" {>= "2.0.0"}