[SE-3111] Use GET instead of POST to retrieve audio sequences

[toxinu]

This merge request is about using GET method instead of POST to retrieve audio sequences.

Jira tickets

• SE-3111
• LX-1294

Testing instructions

Testing instructions

• :warning:️ You need to have labxchange-xblocks installed before
• Create an audio asset with a Soundcloud embed code
• Edit it and add a transcript
• Add another different transcript
• View the audio asset and check that you can see the different transcripts and change between them
• Check that when you change language, new sequences are retrieved using a GET request like that:

/api/xblock/v2/xblocks/lb:LabXchange:3877d1c2:lx_audio:1/handler/3-8a2dfb77df1a0847fb40/sequences/?lang=en

Reviewers

• @s0b0lev

[s0b0lev]

@toxinu +1 looks good

• [x] I tested this: followed test instructions
• [x] I read through the code