Add the ability to read the media file type from HTTP header for playback

How it works today:
media_cache tries to parse out the extension of the media file to be played
from the URI provided to Asterisk while caching the file.

What's expected:
Better will be to have Asterisk get extension from other ways too. One of the
common ways is to get the type of content from the CONTENT-TYPE header in the
HTTP response for fetching the media file using the URI provided.

Steps to Reproduce:
Provide a URL of the form: http://host/media/1234 to Asterisk for media
playback. It fails to play and logs show the following error line:

[Sep 15 15:48:05] WARNING [29148] [C-00000092] file.c:
File http://host/media/1234 does not exist in any format

Scenario this issue is blocking:
In the case where the media files are stored in some cloud object store,
following can block the media being played via Asterisk:

Cloud storage generally needs authenticated access to the storage. The way
to do that is by using signed URIs. With the signed URIs there's no way to
preserve the name of the file.
In most cases Cloud storage returns a key to access the object and preserving
file name is also not a thing there

ASTERISK-27286

 Reporter: Gaurav Khurana

Change-Id: I1b14692a49b2c1ac67688f58757184122e92ba89

formats/format_pcm.c

@@ -507,6 +507,7 @@ static struct ast_format_def alaw_f = {
 static struct ast_format_def pcm_f = {
 	.name = "pcm",
 	.exts = "pcm|ulaw|ul|mu|ulw",
+	.mime_types = "audio/basic",
 	.write = pcm_write,
 	.seek = pcm_seek,
 	.trunc = pcm_trunc,