[IPU] Add hooks for IPU lifecycle 4/5

[SeanNaren]

What does this PR do?

Adds hooks to the accelerator to allow the IPU accelerator to onload/deload models at the end of each stage.

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[codecov]

Codecov Report

Merging #7864 (1f846a3) into master (ea71cf4) will decrease coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #7864   +/-   ##
======================================
- Coverage      88%     88%   -0%     
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  Files         202     202           
  Lines       13096   13121   +25     
======================================
+ Hits        11515   11527   +12     
- Misses       1581    1594   +13     

[kaushikb11]

LGTM!