Install ddtrace via datadog-setup.php on PHP 7.0+

[Teko012]

On PHP 7.0+ this PR switches the ddtrace installation path from the existing PECL + Cargo build to Datadog's official installer, datadog-setup.php. The PECL/Cargo path is preserved for PHP <7.0 and as a fallback when a user pins ddtrace to a version below 1.0.0.

Why

• datadog-setup.php is Datadog's supported install path for the PHP tracer. Using it keeps the installation aligned with Datadog's release artifacts and version-pinning rules instead of relying on PECL's mirror of datadog/dd-trace.
• It can co-install the companion modules (ddappsec, datadog-profiling) in lockstep with the matching tracer build, which is awkward to do via PECL.
• It avoids building Rust from source via Cargo for the common case, which currently pulls curl-dev automake libtool (Alpine) or libssl libcurl4-openssl-dev automake libtool (Debian) and adds noticeable build time/image size.

What changes

installRemoteModule() — the ddtrace) branch (install-php-extensions)

The selection logic is reorganized around the PHP version:

• PHP <7.0 — unchanged path: build from source via PECL + installCargo. If a user explicitly requests ddtrace-1.0.0 or newer on PHP <7.0, the script now errors out (ddtrace <version> requires PHP 7.0 or later) instead of silently failing later. With no version supplied, it still defaults to 0.75.0 (newer 0.x releases refuse PHP 5 in their configure script).
• PHP 7.0+ with an explicit pre-1.0.0 version — keep using the legacy installCargo path so older 0.x releases stay reproducible.
• PHP 7.0+, default or 1.0.0+ — call the new installDDTrace helper and set installRemoteModule_manuallyInstalled=2 so the surrounding code skips the standard PECL pipeline (this is the same convention used for other manually-installed modules like blackfire).

PECL stability flags (stable, beta, …) are still resolved via resolvePeclStabilityVersion before any of the branches above run.

New installDDTrace() helper (install-php-extensions)

installDDTrace [version]

• Downloads datadog-setup.php from the corresponding GitHub release:
  • no version → https://github.com/DataDog/dd-trace-php/releases/latest/download/datadog-setup.php
  • version X.Y.Z → https://github.com/DataDog/dd-trace-php/releases/download/X.Y.Z/datadog-setup.php
• Runs it as php datadog-setup.php --php-bin=php [extra args].
• Honors two new environment variables (see below) to optionally append --enable-appsec and/or --enable-profiling.
• Uses curl $IPE_CURL_FLAGS -sSLf for the download so the existing IPE_INSECURE=1 toggle keeps working, and errors out cleanly with a ### ERROR ### Failed to download … message if the download fails.
• Cleans up the temporary datadog-setup.php once the install completes.

New environment variables (README.md)

Variable	Effect
IPE_DD_APPSEC=1	Pass --enable-appsec to datadog-setup.php, installing the ddappsec module alongside ddtrace. Requires PHP 7.0+ and the 1.x tracer line.
IPE_DD_PROFILING=1	Pass --enable-profiling to datadog-setup.php, installing the datadog-profiling module. Requires PHP 7.1+ on Alpine 3.13+ (any Debian works) and the 1.x tracer line.

Both follow the existing IPE_* env-var conventions (accept 1, y…, Y…).

buildRequiredPackageLists() — ddtrace@alpine and ddtrace@debian (install-php-extensions)

The development packages that were unconditionally pulled in for ddtrace are now gated behind PHP_MAJMIN_VERSION -lt 700, because they're only needed by the Cargo build path:

• Alpine: curl-dev automake libtool — installed only on PHP <7.0.
• Debian: $buildRequiredPackageLists_libssl libcurl4-openssl-dev automake libtool — installed only on PHP <7.0.

For PHP 7.0+ the datadog-setup.php flow installs the prebuilt tracer binary, so none of these dev packages are needed.

Test script: scripts/tests/ddtrace

Adds an executable PHP test that:

1. Verifies ddtrace_version() is defined and prints the resolved version.
2. If IPE_DD_PROFILING was set during install, verifies the datadog-profiling extension is loaded.
3. If IPE_DD_APPSEC was set during install, verifies the ddappsec extension is loaded.

The script exits non-zero on any failure so it can be wired into the existing extension test matrix.

Backwards compatibility

• install-php-extensions ddtrace on PHP <7.0 behaves exactly as before (default 0.75.0, Cargo build, same build deps).
• install-php-extensions ddtrace-<0.x.y> on PHP 7.0+ keeps the previous Cargo-based path.
• The only behavioral change for existing users on PHP 7.0+ without a pinned version is the switch from the PECL/Cargo build to the official datadog-setup.php install — which yields the same ddtrace extension but no longer leaves curl-dev/libcurl4-openssl-dev/automake/libtool lingering as runtime-installed packages.

Closes #1163.

[Teko012]

@mlocati What do you think about this?