Deprecate special handling for quoted values for TLS flags

The `--tlscacert`, `--tlscert`, and `--tlskey` command-line flags had
non-standard behavior for handling values contained in quotes (`"` or `'`).
Normally, quotes are handled by the shell, for example, in the following
example, the shell takes care of handling quotes before passing the values
to the `docker` CLI:

    docker --some-option "some-value-in-quotes" ...

However, when passing values using an equal sign (`=`), this may not happen
and values may be handled including quotes;

    docker --some-option="some-value-in-quotes" ...

This caused issues with "Docker Machine", which used this format as part
of its `docker-machine config` output, and the CLI carried special, non-standard
handling for these flags.

Docker Machine reached EOL, and this special handling made the processing
of flag values inconsistent with other flags used, so this behavior is
deprecated. Users depending on this behavior are recommended to specify
the quoted values using a space between the flag and its value, as illustrated
above.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Author: thaJeztah

docs/deprecated.md

@@ -53,6 +53,7 @@ The following table provides an overview of the current status of deprecated fea
 
 | Status     | Feature                                                                                                                            | Deprecated | Remove |
 |------------|------------------------------------------------------------------------------------------------------------------------------------|------------|--------|
+| Deprecated | [Special handling for quoted values for TLS flags](#special-handling-for-quoted-values-for-tls-flags)                              | v28.4      | v29.0  |
 | Deprecated | [Empty/nil fields in image Config from inspect API](#emptynil-fields-in-image-config-from-inspect-api)                             | v28.3      | v29.0  |
 | Deprecated | [Configuration for pushing  non-distributable artifacts](#configuration-for-pushing-non-distributable-artifacts)                   | v28.0      | v29.0  |
 | Deprecated | [`--time` option on `docker stop` and `docker restart`](#--time-option-on-docker-stop-and-docker-restart)                          | v28.0      | -      |
@@ -122,6 +123,39 @@ The following table provides an overview of the current status of deprecated fea
 | Removed    | [`--run` flag on `docker commit`](#--run-flag-on-docker-commit)                                                                    | v0.10      | v1.13  |
 | Removed    | [Three arguments form in `docker import`](#three-arguments-form-in-docker-import)                                                  | v0.6.7     | v1.12  |
 
+
+### Special handling for quoted values for TLS flags
+
+**Deprecated in Release: v28.4**
+**Target For Removal In Release: v29.0**
+
+The `--tlscacert`, `--tlscert`, and `--tlskey` command-line flags had
+non-standard behavior for handling values contained in quotes (`"` or `'`).
+Normally, quotes are handled by the shell, for example, in the following
+example, the shell takes care of handling quotes before passing the values
+to the `docker` CLI:
+
+```console
+docker --some-option "some-value-in-quotes" ...
+```
+
+However, when passing values using an equal sign (`=`), this may not happen
+and values may be handled including quotes;
+
+```console
+docker --some-option="some-value-in-quotes" ...
+```
+
+This caused issues with "Docker Machine", which used this format as part
+of its `docker-machine config` output, and the CLI carried special, non-standard
+handling for these flags.
+
+Docker Machine reached EOL, and this special handling made the processing
+of flag values inconsistent with other flags used, so this behavior is
+deprecated. Users depending on this behavior are recommended to specify
+the quoted values using a space between the flag and its value, as illustrated
+above.
+
 ### Empty/nil fields in image Config from inspect API
 
 **Deprecated in Release: v28.3**