Release v0.3.0

[mniestroj]

Notes:

• NCS was not bumped to the latest v2.1.0 yet. The reason is MBEDTLS_DTLS compatibility with TF-M and SPM changes in NCS.
• samples/dfu/ is not reliable with mimxrt1060_evkb - it still results in crashes; problem seems to be some kind of race condition, because adding LOG_INF() statements in Zephyr init process allows to workaround that issue.

[github-actions[bot]]

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[mniestroj]

@szczys @ChrisGammell Please review Changelog updates.