refactor: do not add ~service in createOOBOffer method

[TimoGlastra]

When calling createOutOfBand offer and then attaching it to the oob invitation would create two set of keys. To overcome this the creating of an offer does not create the keys for the exchange anymore. Instead you just get the message that is not associated with a connection yet. Then you can:

• call oob.createInvitation to create an oob invitation
• call oob.createLegacyConnectionlessInvitation to create a pre-aip connectionless invitation by attaching the ~service decorator.

BREAKING CHANGE: with the addition of the out of band module credentials.createOutOfBandOffer is renamed to credentials.createOffer and no longer adds the ~service decorator to the message. You need to call oob.createLegacyConnectionlessInvitation afterwards to use it for AIP-1 style connectionless exchanges. See Migrating from AFJ 0.1.0 to 0.2.x for detailed migration instructions.

[TimoGlastra]

@NB-MikeRichardson please take a look at the changes, this touches the credentials module

[codecov-commenter]

Codecov Report

Merging #772 (e875d5d) into main (0c1423d) will increase coverage by 0.02%.
The diff coverage is 95.83%.

@@            Coverage Diff             @@
##             main     #772      +/-   ##
==========================================
+ Coverage   87.59%   87.61%   +0.02%     
==========================================
  Files         437      437              
  Lines       10806    10779      -27     
  Branches     1900     1892       -8     
==========================================
- Hits         9465     9444      -21     
+ Misses       1279     1273       -6     
  Partials       62       62              

Impacted Files	Coverage Δ
.../modules/credentials/services/CredentialService.ts	100.00% <ø> (ø)
packages/core/src/modules/oob/OutOfBandModule.ts	87.16% <90.90%> (-0.29%)	⬇️
.../core/src/modules/credentials/CredentialsModule.ts	91.23% <100.00%> (+0.42%)	⬆️
...les/credentials/protocol/v1/V1CredentialService.ts	87.09% <100.00%> (+0.27%)	⬆️
...les/credentials/protocol/v2/V2CredentialService.ts	94.15% <100.00%> (+0.56%)	⬆️
...re/src/storage/didcomm/DidCommMessageRepository.ts	88.88% <100.00%> (+0.88%)	⬆️

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[berendsliedrecht]

Nothing major, just two code cleanup things.