chore: switch to SPDX license headers

[Manvi2402]

Description

Switch all Python source files from the full 13-line Apache 2.0 license
header to the shorter 2-line SPDX format.

Fixes #4521

This is a housekeeping/chore change. The SPDX format is legally and
functionally equivalent to the full Apache 2.0 header. Other OTel SDKs
have already made this change:

• Go SDK: opentelemetry-go#4987
• Java SDK: already uses SPDX format

588 .py files updated. 2 files with Google LLC copyright were intentionally
left unchanged.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• Ran the replacement script in dry-run mode to verify all files
• Confirmed Google LLC copyrighted files were not modified
• No CI checks for license headers exist in this repo

Does This PR Require a Core Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

See contributing.md for styleguide, changelog guidelines, and more.

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[tammy-baylis-swi]

Hi @Manvi2402 great to see more contributions from you!

Several of the lint jobs are failing. I suspect it might be the script used and/or using a Windows machine:

C0328: Unexpected line ending format. There is 'CRLF' while it should be 'LF'. (unexpected-line-ending-format)

Please update the files to end in \n not \r\n.

[tammy-baylis-swi]

I've noticed also there is a duplicate #4533 (review) cc @MikeGoldsmith

[Manvi2402]

Thanks for the kind words @tammy-baylis-swi ! I had a great time working on this — learned a lot about SPDX headers and CI checks in the process. I'll go ahead and close my PR #4532 since #4533 is already good to go. Looking forward to contributing more!

[MikeGoldsmith]

Ah, sorry @Manvi2402 - thank you for your effort ❤️