tag: add GstMeta for KLV metadata

Can be used to attach arbitrary metadata to buffers,
such as timestamps, GPS data, etc.

See ITU Recommendation BT.1563-1 or SMPTE 336M for the
KLV standard, and MISB EG 0902 (MISB Minimum Metadata Set)
and other MISB standards and recommended practices for
examples of KLV metadata local data sets for a variety
of use cases. Also SMPTE ST380.

Fixes #410.
8 jobs for klv-meta in 17 minutes and 15 seconds (queued for 3 seconds)
latest
Status Job ID Name Coverage
  Preparation
passed #121104
gst indent

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passed #121103
manifest

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  Build
passed #121105
build fedora x86_64

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  Test
passed #121106
check fedora

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  Full Builds
passed #121107
build android arm64 api28

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passed #121109
build cerbero cross win32

00:09:37

passed #121110
build cerbero cross win64

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passed #121108
build cerbero fedora x86_64

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