chore: move alpha_texture from PBRMaterial to UnlitMaterial

[AlejandroAlvarezMelucciDCL]

Addresses the SDK part of issue #240

Related PRs:
E@: decentraland/unity-explorer#2482
Protocol: decentraland/protocol#223

[cloudflare-workers-and-pages]

Deploying js-sdk-toolchain with    Cloudflare Pages

Latest commit:	79972ef
Status:	✅  Deploy successful!
Preview URL:	https://29988a0a.js-sdk-toolchain.pages.dev
Branch Preview URL:	https://chore-move-alphatexture-from.js-sdk-toolchain.pages.dev

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[github-actions]

Test this pull request

• The @dcl/sdk package can be tested in scenes by running

  npm install "https://sdk-team-cdn.decentraland.org/@dcl/js-sdk-toolchain/branch/chore/move-alphaTexture-from-PBRMaterial-to-UnlitMaterial/dcl-sdk-7.6.3-11407293123.commit-683d0d0.tgz"

• To test with npx init

  export SDK_COMMANDS="https://sdk-team-cdn.decentraland.org/@dcl/js-sdk-toolchain/branch/chore/move-alphaTexture-from-PBRMaterial-to-UnlitMaterial/dcl-sdk-commands-7.6.3-11407293123.commit-683d0d0.tgz"
  npx $SDK_COMMANDS init

• The @dcl/inspector package can be tested by visiting this url

  • Or by installing it via NPM

  npm install "https://sdk-team-cdn.decentraland.org/@dcl/js-sdk-toolchain/branch/chore/move-alphaTexture-from-PBRMaterial-to-UnlitMaterial/@dcl/inspector/dcl-inspector-7.6.3-11407293123.commit-683d0d0.tgz"

• The /changerealm command to test test in-world

  /changerealm https://sdk-team-cdn.decentraland.org/ipfs/chore/move-alphaTexture-from-PBRMaterial-to-UnlitMaterial-e2e
  

• You can preview this build entering:
  https://playground.decentraland.org/?sdk-branch=chore/move-alphaTexture-from-PBRMaterial-to-UnlitMaterial

[pravusjif]

• The lint has to be fixed
• Remember to correct the protocol package before merging this PR (After the protocol PR is merged)