feat(synth): add datastore v1 admin api

[zamnuts]

This is part 1 of 2 for resolving #685:

• Updates synth to include v1 admin proto generation
• Exports DatastoreAdminClient

Implementation of RPC manual wrappers will come in a second PR.

[codecov]

Codecov Report

Merging #686 into master will decrease coverage by 0.54%.
The diff coverage is 97.75%.

@@            Coverage Diff             @@
##           master     #686      +/-   ##
==========================================
- Coverage   99.40%   98.85%   -0.55%     
==========================================
  Files           7       10       +3     
  Lines        6175     7243    +1068     
  Branches      426      438      +12     
==========================================
+ Hits         6138     7160    +1022     
- Misses         36       81      +45     
- Partials        1        2       +1     

Impacted Files	Coverage Δ
src/v1/datastore_admin_client.ts	97.74% <97.74%> (ø)
src/v1/index.ts	100.00% <100.00%> (ø)
.prettierrc.js	0.00% <0.00%> (ø)
.mocharc.js	78.57% <0.00%> (ø)

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