Switch to SPDX license headers

[MikeGoldsmith]

Description

All Python files in this repo currently use the full Apache 2.0 license header (13 lines):

# Copyright The OpenTelemetry Authors
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

Other OTel SDKs have already moved to the shorter SPDX format (2 lines):

# Copyright The OpenTelemetry Authors
# SPDX-License-Identifier: Apache-2.0

This is functionally and legally equivalent. It reduces visual noise and is consistent with the direction other SDKs have taken.

Precedent

• Go SDK: Simplify the license header opentelemetry-go#4986 / [chore] Simplify the license header opentelemetry-go#4987
• Java SDK: Already uses SPDX format

Scope

~779 .py files in this repo would be updated.

Steps

• Write a script to replace the 13-line Apache header with the 2-line SPDX header across all .py files
• Verify no files are missed (check for header variations)
• Update any CI or pre-commit checks that validate the header format
• Submit PR (single large PR, best timed during a quiet period to minimize rebase conflicts)
• Update contributing docs if they reference the old header format
• Coordinate with opentelemetry-python-contrib to do the same

Notes

There is no runtime performance impact — Python strips comments during bytecode compilation. The benefit is purely reduced boilerplate and consistency with other OTel SDKs.

[Dipanshusinghh]

@MikeGoldsmith This looks like a solid move — cutting down boilerplate and keeping things consistent with other OpenTelemetry SDKs makes a lot of sense.
One thing to watch out for: some files might have slight variations in their existing headers, so the replacement script may need to handle those cases carefully.
Also, it could be worth adding a CI or pre-commit check for SPDX headers going forward, just to keep everything consistent and avoid drift over time.